By Heather Haddon

McDonald's Corp. said it is suing former Chief Executive Steve Easterbrook and seeking to recoup tens of millions it paid him in severance and benefits, alleging that he lied to the board about sexual relationships with employees before his ouster last fall.

The fast-food giant dismissed Mr. Easterbrook without cause in November 2019, following an investigation into his conduct. Investigators found he had a short-term, consensual relationship with an employee over text and video, but Mr. Easterbrook denied any physical sexual relationships with McDonald's employees, according to the complaint filed Monday.

McDonald's reopened the matter after it received an anonymous tip in July about a relationship between Mr. Easterbrook and an employee, according to the suit. An investigation found that Mr. Easterbrook allegedly engaged in three other relationships with employees that were sexual in nature, including the one that triggered the inquiry. Investigators found that Mr. Easterbrook destroyed evidence about the sexual relationships and lied about his behavior during the initial investigation last fall, the complaint said.

Because McDonald's decided to fire Mr. Easterbrook without cause, he received severance and benefits that he could have been denied had the board found him at fault. Mr. Easterbrook's compensation, benefits and stock were potentially worth nearly $42 million, according to an analysis at the time by executive-pay firm Equilar.

The company also alleged that Mr. Easterbrook approved a stock grant to an employee with whom he was having a sexual relationship. The grant was valued at hundreds of thousands of dollars, according to the suit.

"McDonald's does not tolerate behavior from any employee that does not reflect our values," Chris Kempczinski, who succeeded Mr. Easterbrook as CEO last November, wrote in a message to the company on Monday.

At the time of his firing, Mr. Easterbrook said the consensual affair was a mistake, and that he agreed with the board's decision to fire him. Mr. Easterbrook also said at the time that he hadn't engaged in other relationships with employees, according to McDonald's.

Mr. Easterbrook, appointed CEO in 2015, helped McDonald's streamline operations and modernize. He also took part in a culture of partying and fraternizing among some senior managers and rank-and-file employees, The Wall Street Journal previously reported citing some former employees and people currently connected to the company.

McDonald's said in the suit that its investigation found dozens of nude and sexually explicit photographs and videos of women, including employees, sent from Mr. Easterbrook's corporate email account to a personal one. Mr. Easterbrook had deleted the photos from his company-issued phone, and they weren't discovered during the company investigation that triggered his firing, according to the complaint.

McDonald's said in the complaint, to be filed Monday in the Court of Chancery of the State of Delaware, that Mr. Easterbrook breached his fiduciary duties as a company officer and committed fraud. The company said it is seeking to recover the amount it paid Mr. Easterbrook in compensation and severance benefits. It is also seeking to prevent Mr. Easterbrook from exercising stock options.

Some shareholder groups had criticized the board's decision to fire Mr. Easterbrook without cause despite conduct that violated longstanding company policies forbidding relationships with direct and indirect reports. Proxy-advisory firm Glass Lewis advised shareholders earlier this year to vote against the company's executive pay package given the severance package afforded to Mr. Easterbrook.

That payout included $700,000 in cash severance to Mr. Easterbrook. Total compensation, including equity awards, amounted to $17.4 million in 2019. The company's stockholders in May approved total compensation and equity awards for Mr. Easterbrook. The suit doesn't specify an exact sum McDonald's seeks to recover. The company wrote in the suit that it is seeking the annulment of the severance agreement, damages and the return of Mr. Easterbrook's stock and cash awards.

McDonald's said in the complaint that to have fired Mr. Easterbrook for cause last year, it would have had to prove that his behavior had constituted "dishonesty, fraud, illegality or moral turpitude." At the time, board members felt they lacked evidence to justify firing the CEO for cause, the complaint said.

Mr. Kempczinski, who served under Mr. Easterbrook as the head of McDonald's U.S. business, pledged to overhaul the company's culture after assuming the job in November. Mr. Kempczinski pledged to renew company values during a virtual company summit late last month. McDonald's in March hired Heidi Capozzi, previously the senior vice president of human resources for Boeing Co., as its new global chief people officer.

Write to Heather Haddon at heather.haddon@wsj.com