The chief executive of NBCUniversal has left the US entertainment giant after acknowledging "an inappropriate relationship" with a colleague, parent company Comcast announced Sunday.

Comcast said in a statement that it came to a "mutual decision" with Jeff Shell for him to step down "effective immediately" and "following the company's investigation led by outside counsel into a complaint of inappropriate conduct."

NBCUniversal, which was fully acquired by Comcast in 2013, owns a broad portfolio of television news and entertainment networks, as well as a motion picture studio, theme parks and a premium streaming service.

"Today is my last day as CEO of NBCUniversal," Shell, 57, said in the Comcast statement.

He acknowledged having "had an inappropriate relationship with a woman in the company."

"I'm truly sorry I let my Comcast and NBCUniversal colleagues down, they are the most talented people in the business," he added.

Shell had been with the New York-based conglomerate for just under two decades, and had served as CEO since January 2020.

Earlier in his career at Universal Films, Shell oversaw some of the studios biggest franchises such as Fast & Furious and Jurassic World.

In an internal memo to employees, shared with AFP, Comcast CEO Brian Roberts said: "We built this company on a culture of integrity."

"When our principles and policies are violated, we will always move quickly to take appropriate action, as we have done here."

The memo did not name an immediate successor, but said that senior executives at NBCUniversal would report directly to Comcast President Mike Cavanagh.

The website of financial news channel CNBC, a part of NBCUniversal, cited unnamed sources as saying the complaint against Shell "was filed by the woman with who Shell shared the 'inappropriate relationship.'"

Shell is the second senior executive to leave the company in the past three years over inappropriate conduct, and as Hollywood continues to clamp down on previously unchecked misbehavior by its moguls.

In 2020, the company's vice chairman Ron Meyer left the company after admitting to having an affair and paying the woman a settlement.

The issue has not been isolated to NBCUniversal: Jeff Zucker, the former president of CNN, abruptly left his role in February 2022 for not having disclosed a relationship with a colleague.

Comcast is due to report its first quarter financial results on Thursday morning.

Analysts will be closely watching the results of its streaming platform, Peacock, which has struggled to compete with rivals Netflix and Disney+.

In his statement to employees, Roberts said that "NBCUniversal is performing extremely well operationally and financially."

Entertainment giants are facing increasing pressure to maintain growth of subscribers for their streaming services.

Disney announced layoffs of 7,000 employees in February after the storied company founded by Walt Disney saw its first ever fall in subscribers.

For its part, archrival Netflix last week said its number of subscribers hit a record high of 232.5 million in the first quarter of the year, posting a quarterly profit of $1.3 billion.