BRITNEY Spears has reportedly accused Justin Timberlake of cheating on her with another celebrity during their romance.

The singer, 41, allegedly made the claims about her ex, 42, in her upcoming memoir, The Woman In Me.

Britney Spears has reportedly accused Justin Timberlake of cheating on her with another celebrity during their romance. Credit: Barry King/WireImage

Britney didn’t name the woman as she didn’t want to embarrass her, a source claimed to TMZ. Credit: 2016 Anthony Harvey/Getty

Justin, pictured last month at the Ryder Cup golf in Italy, first met Britney as teen stars of the Mickey Mouse Club. Credit: Andrew Redington/Getty Images

Justin dated Britney from 1999 to 2002, having met her on the set of TV’s The Mickey Mouse Club in 1992.

Britney didn’t name the person who Justin allegedly cheated on her with in the book, according to TMZ.

The Overprotected hitmaker reportedly didn’t want to embarrass the other woman, who now has a family.

The U.S. Sun has contacted representatives for Britney and Justin for comment.

Britney’s claims are a far cry from the narrative that was set in 2002 by Justin’s song, Cry Me A River, which he released shortly after their split.

The lyrics and music video led fans to believe that Britney had cheated on him.

The clip showed Justin and a blond actress dressed suspiciously like the songstress as she cheated on him.

The lyrics stated: “Told me you loved me / Why did you leave me all alone? / Now you tell me you need me / When you call me on the phone.”

Justin denied that the song was about Britney in an interview with Carson Daly.

Britney’s cheating claims come one day after it was reported that Justin got her pregnant and that she had an abortion.

She reportedly fell pregnant in late 2000 when they were both 19.

The Overprotected singer wanted to have Justin’s baby but felt “conflicted,” she wrote.

“It was a surprise, but for me, it wasn’t a tragedy. I loved Justin so much. I always expected us to have a family together one day,” Britney penned, according to People.

“This would just be much earlier than I’d anticipated. But Justin definitely wasn’t happy about the pregnancy.

“He said we weren’t ready to have a baby in our lives, that we were way too young. I’m sure people will hate me for this, but I agreed not to have the baby. I don’t know if that was the right decision.

“If it had been left up to me alone, I never would have done it. And yet Justin was so sure that he didn’t want to be a father.”

The star said the abortion was “one of the most agonizing things I have ever experienced in my life” in the memoir – which is set for release on October 24.

Britney had her first child, son Sean Preston, with her now ex-husband Kevin Federline in 2005 and her second son, Jayden James, in 2006.

Justin went on to marry The Illusionist actress Jessica Biel, 41, in 2012 and the couple share sons Silas, eight, and Phineas, three.

The U.S. Sun exclusively revealed this week that Justin and Jessica will have been left reeling from Britney’s bombshell claims.

A source said: “Justin owns who he was when he and Britney were together, even though his personality, career, lifestyle, and personal priorities are radically different now, 20 years later.

“This book is a nightmare for him because of how it throws the whole family into chaos. The timing stings just as much as the revelation itself.”

The insider continued: “Justin had a big fall planned with new music on deck, more work with his old friends in ‘NSYNC, and of course, the next installment of the Trolls franchise, which has been a huge moneymaker for Justin over the last several years.”

Britney pictured breaking down in tears on American television in 2003 when she was asked about the break up of her relationship with Justin Timberlake. Credit: SPLASH NEWS

They dated from 1999 until 2002. Credit: Jeffrey Mayer/WireImage

Britney also claimed she fell pregnant with Justin’s baby and had an abortion. Credit: GETTY

Justin and his wife Jessica Biel are reportedly ‘reeling’ from the bombshells in Britney’s book. Credit: Getty