"I wanted to show him how great and fun I could be," Moore revealed in her upcoming memoir.
Demi Moore and Ashton Kutcher's marraige ended somewhat acrimoniously in 2013, after separating for two years prior.
At the time, the reasons behind the divorce were somewhat obscured, but in a new tell-all memoir, Moore has revealed that the beginning of the end of the marriage came about when Kutcher slept with a 21-year old woman, whom he met while bowling with Moore's daughter, Rumer Willis.
According to Moore's memoir, which was excerpted in Us Weekly, Kutcher then claimed that the fact that couple had engaged in threesomes during the marriage was a reasonable defence for sleeping with the woman. "Because we had brought a third party into our relationship, Ashton said, that blurred the lines and, to some extent, justified what he’d done,” she claimed.
Moore also revealed in the memoir that she agreed to the threesomes for the wrong reasons, saying that she "wanted to show him how great and fun" she could be, and that she regretted taking part in them. Kutcher was unfaithful at least twice in their marriage, according to Moore, and said that she learned about one of them from a Google alert.
Kutcher has so far made no statement on Moore's claims, or the substance of her memoirs, and HarperCollins - the publisher behind the memoir - hasn't responded to media comments on the allegations either.
Kutcher and Moore were married in 2003, and stayed together for ten years, filing for divorce in 2013 after Kutcher moved out of their home in 2011. Kutcher then married again in 2015, reuniting with his co-star from 'That '70s Show', Mila Kunis.
Moore's memoir, 'Inside Out', is on sale from September 24th.