The politicians, business leaders and foreign envoys in attendance heaped praise on the company’s octogenarian executive chairman, Kwek Leng Beng, who built a family fortune estimated at $11.5 billion and made deals with the likes of Donald Trump. Guests at the black-tie dinner savored abalone, bird’s nest soup and lobster, while dancers and musicians performed on a stage.

At the head table, the tycoon, clad in a blue tuxedo, reigned with his wife, Cecilia.

But there was another woman in the ballroom, wearing a red dress, whose presence wasn’t welcome to some in the family.

Catherine Wu, a Juilliard-trained pianist and former television host in her native Taiwan, was well-known to company executives for her close relationship with the chairman. Senior executives had long bristled at what they saw as her interference in the hotel business, according to people familiar with the matter. But until this moment, she had largely shunned the limelight and avoided public company events. The internal complaints about her outsize influence remained unknown to the public.

Now Wu was thrusting herself into the spotlight, introducing herself to the dignitaries—including Singapore’s prime minister-in-waiting—and posing for photos with them. Onlookers blanched. People sympathetic to Cecilia Kwek and concerned about Wu’s influence at the company thought Wu, by attending the gala, had crossed a line.

Earlier this year, the tensions that seethed at the event burst into the open.

The chairman’s elder son and chosen successor, Sherman Kwek, 49, and his allies moved to add new directors to the board, a maneuver he later said was meant to eliminate Wu’s influence at the family business, called City Developments Ltd., or CDL for short.

Kwek Leng Beng, shown here in April, oversees a family fortune that Forbes estimated last year to be worth $11.5 billion.Sherman Kwek is the chief executive of City Developments Ltd. and his father’s designated successor.

“She has been interfering in matters going well beyond her scope, and she wields and exercises enormous influence,” Sherman Kwek said in a statement on behalf of the majority of the board, issued in February after the feud erupted into public view. “Due to her long relationship with the chairman, efforts that were made to manage the situation were done sensitively, but to no avail.”

Kwek Leng Beng fought back by trying to dismiss his son as chief executive and suing him for allegedly trying to usurp power—something that Sherman denies. The elder Kwek later said Wu had contributed to the business’s success and decried his son’s “unproven insinuations.”

Wu, in her first public comments on the matter, told The Wall Street Journal in an email this month that her relationship to the chairman was “purely professional.” She said the elder Kwek had “asked for and considered my feedback on business ideas,” adding that she had “had no role in the decision-making process” at CDL. She said the dispute was between board members and “has nothing to do with me, although some parties have used my name to stoke the flames.”

Catherine Wu has been a longtime adviser to the elder Kwek.

Weeks after the clash, the sides agreed to a truce. The public warring had done no good for a company dealing with high debt and a lackluster share price.

In March, the elder Kwek announced Wu’s resignation as an adviser at CDL’s hotel subsidiary and dropped his lawsuit. His son remains CEO, backed by additional allies on the board and a company resolution declaring that Wu has no power to influence or direct management and staff at CDL and its hotel business.

But Wu is still in contact with one person at CDL: the 84-year-old chairman. People at the company say the elder Kwek and Wu, who turns 66 this month, have recently been seen meeting at CDL-owned properties. It means, the people say, that the saga is far from over.

Strictly business

Just north of the equator, six million people swelter in a city-state about a quarter of Rhode Island’s size. A disproportionate many are millionaires, and some of Singapore’s richest residents are members of family businesses that predate the nation’s 60 years of independence.

As Singapore transformed from a colonial outpost into a hub of prosperity, the Kwek clan was there to help build it every step of the way.

Kwek Leng Beng’s father, Kwek Hong Png, started a construction-materials store in 1941, when Singapore was a British colony. Kwek Leng Beng joined the business in 1963 and was given stern training by his father, as he and Cecilia recounted in an authorized biography, “Strictly Business.”

Singapore in the 1940s. The Kwek family has helped transformed the city over the past several decades.

When the couple were dating, Kwek Leng Beng’s father imposed a curfew. “The old man wanted him to be in bed by 9 p.m.,” Cecilia said in the biography.

Kwek Leng Beng and Cecilia, both London-trained lawyers, wed in 1970. They spent much of the next few years in Singapore in the lobby of the company’s first hotel, where she’d drink hot chocolate while he quizzed staff about occupancy rates and mingled with guests for feedback, the biography said.

By the 1990s, Kwek was in charge of a flourishing family business that would eventually expand to more than 150 hotels worldwide, including Millennium hotels in New York and London. It controlled so much real estate in Singapore at one point that he was dubbed “Kwek Land Bank.”

As part of a venture with a Saudi prince, CDL bought New York City’s Plaza Hotel, the iconic establishment next to Central Park that’s played host to royalty, presidents and the fictional Kevin McCallister in the 1992 movie “Home Alone 2.” They paid $325 million to buy it from Trump in 1995, and then sold it nine years later for $675 million. In the mid-2000s, Kwek advised Las Vegas casino magnate Sheldon Adelson on building the Marina Bay Sands casino resort in Singapore. Today, it is a symbol of the island nation’s skyline.

Kwek Leng Beng, second from the left in this 2007 photo, advised Sheldon Adelson, far left, on the building of the Marina Bay Sands casino resort in Singapore.

Eyes and ears

As the years went by, an adviser by Kwek’s side became impossible for insiders to ignore. Catherine Wu, who holds a doctorate in music from New York University, was in her early 30s when she met Kwek in 1992 at a dinner party. She was well-known in Taiwan as a TV host and pianist, having released albums under the name Ingrid Wu with tracks such as “His Lover” and “I’ll Decide Before Dawn Whether I Love You.”

At the dinner, Kwek quizzed Wu about politics, economics and music “to see if my mind was flexible and if my answers were consistent,” Wu told a Singaporean newspaper last year. “Fortunately, I answered articulately.”

Catherine Wu released piano albums in Taiwan under the name Ingrid Wu.

Wu decided to move to Singapore that same year, she told the newspaper, saying she wanted to escape attention by relocating to a place where she wasn’t well-known, and that the city-state’s East-meets-West vibes suited her. In her email to the Journal, Wu described music as her former career and said she had spent 30 years in business amassing professional achievements.

Kwek invited her to hotel-management meetings and events. “The chairman would scold me from time to time, but I wouldn’t take it to heart,” Wu said in the newspaper interview. “If a successful person is willing to put in the thought and energy to scold you, it means you are teachable.”

Paid not by the company but by Kwek himself, Wu acted as the chairman’s “eyes and ears” and often accompanied him to visit properties around the world, according to a 2018 U.K. labor tribunal ruling. The tribunal was investigating a dispute involving a former employee who accused a CDL subsidiary of unfair dismissal and other wrongdoing, a case the tribunal dismissed.

Some executives and employees—including people who later left the company—bristled at Wu’s conduct, filing complaints against her both internally and to a Singapore government-backed agency, according to people familiar with the matter. These complaints included allegations that Wu berated staff, meddled in business matters beyond her remit and used the elder Kwek’s name to rubber-stamp her decisions, the people said.

Sometimes, executives believed that business decisions they thought had been approved by the chairman were later overruled by Wu. In one instance cited in the complaints, the people said, Wu got the company to halt planned renovations to a hotel in London near the Harrods luxury department store, even though management believed the project would boost revenue and had spent years preparing for it.

Catherine Wu and Kwek Leng Beng at the GeekCon 2024 cybersecurity conference.

Many employees came to believe that Wu was sometimes using one of the elder Kwek’s corporate email accounts to send instructions in his name, people close to CDL said. They said these employees learned to recognize what they believed to be Wu’s imprint on such emails—a more formal and detailed writing style, compared with the elder Kwek’s curt approach, and the signature “Sent from my iPad,” which was notable because the chairman wasn’t known to use an iPad. Kwek declined to comment, while Wu didn’t respond to requests for comment about this matter.

According to the people, some executives expressed unease when one of Wu’s six brothers, a former journalist for a Taiwanese television network, became general manager of the Biltmore Los Angeles in 2018. He had little experience in the hospitality industry, apart from a short stint as a business-development executive in CDL’s hotel subsidiary.

During the brother’s stint as general manager, he, the hotel and a company affiliated with CDL’s hotel subsidiary faced lawsuits from former Biltmore employees over allegations that included discrimination, harassment and wrongful termination, according to court papers. These cases have generally been settled out of court, according to court documents and people close to CDL, and the company didn’t make any public admission of wrongdoing. The brother has stepped aside as general manager and remains an owner’s representative—a supervisory role that oversees the hotel’s operations and liaises between its owner and management.

The brother didn’t respond to requests for comment.

The heir

Senior executives tried for years to persuade Sherman Kwek, the designated successor to the elder Kwek, to directly address the tensions over Wu, say insiders.

Sherman Kwek didn’t see much of his father as a child, as he recounted in his dad’s biography. After studying business at Boston University, he worked in venture capital and investment banking in New York before his father brought him to the family business.

Sherman Kwek had his own issues to deal with. After becoming CDL’s CEO, he had spearheaded a 2019 investment in a Chinese developer that went sour and led to a $1.4 billion write-down. “I wanted to hide my face in the sand” and came close to resigning, he recounted in a speech last year. “I went from hero to zero overnight.”

The younger Kwek retained his father’s support then and went on to strike profitable deals divesting some commercial properties, but he still faced skepticism from investors.

Sherman Kwek and his allies thought they had eased Wu out of the picture when she resigned as a director of CDL’s hotel subsidiary in January 2024, people close to the company say. But in August that year, Wu rejoined the subsidiary as an unpaid board adviser and the Singaporean newspaper published its interview with a headline that called her the elder Kwek’s “grand chamberlain.”

Kwek Leng Beng and his son Sherman Kwek in 2019.

Wu’s return stunned some senior CDL figures and board members, who had to try again to remove her from the business, people close to the company say. They first appealed to the elder Kwek to act, and then—after seeing no results—initiated a move in late January to add new independent directors to the CDL board, the people say.

These efforts eventually led to the public feuding, which drew breathless coverage from local media that documented the boardroom spat blow-by-blow.

Following the truce earlier this year, after which Sherman Kwek continued as chief executive and his father as chairman, Wu now has no official title at the company.

Sherman Kwek remains in the hot seat, facing market pressure to execute plans to pare back CDL’s debt and lift its share price, which still languishes below prepandemic levels.

Watching over him is his father, who remains a revered figure at CDL overseeing a family fortune that Forbes estimated last year to be worth $11.5 billion. The elder Kwek has maintained his contacts with Wu, whose protégés still hold positions in the hotel business, according to people close to CDL. One of these people says the company is looking into past complaints against Wu. This week, CDL said a longserving board member, who sided with the chairman during the feud, will retire from the board at the end of July.

A CDL spokesman said Kwek Leng Beng, Sherman Kwek and the company declined to comment.

Both father and son continue to go into CDL’s headquarters at Republic Plaza, a soaring 66-story skyscraper in Singapore’s business district.

At a public space there, a holographic painting that Sherman Kwek presented to the elder Kwek at the 2023 gala—depicting either the grandfather Kwek, the father or the son depending on the viewing angle—remains on display. Next to it stands a piece of Chinese calligraphy penned by one of Wu’s brothers, which says, “Three generations of blood and sweat, six decades of honor and glory.”

Write to Chun Han Wong at chunhan.wong@wsj.com and Stu Woo at Stu.Woo@wsj.com