Karissa Shannon has claimed Hugh Hefner tried to "force" her to have sex with her twin sister.

The 37-year-old model - who moved into the Playboy Mansion with her sibling Kristina from 2008 to 2010 - admitted she was confused as to why people were shocked by Hefner's widow Crystal Harris' recent claims about "incest" in the bedroom involving the twins and the late media mogul.

Karissa noted she had previously described sex with Hefner as feeling like "assault" and "rape", including an alleged threesome on her 19th birthday, and told the New York Post newspaper's Page Six column: "I figured people would already have assumed that.

"He would try and force me and my sister to have sex with each other.

"Me and my sister never actually did it together. So that's a statement I want to say. Like, really, we never, never had incest[uous] sex. Like, we never did that."

Karissa noted Crystal - who was married to Hefner from December 2012 until his death in September 2017 at the age of 91 - was often present and aware that she and her sister "were faking it".

She said: "We faked it. We faked it every time. And it was horrible. Like, we faked it completely."

However, she claimed Hefner "had no idea" and "thought it was real", so always felt "so happy" because he thought the situation was "beautiful".

She claimed: "He wanted to see it and wanted us to fool around with each other and said that if we really loved each other, we would do it together.

"Me and my sister spoke about it. … We were like, 'Let's just fake it.' "

Karissa feared her own experiences weren't unique and she was particularly worried about Sandy and Mandy Bentley, twins who were regulars at the Playboy Mansion in the early 2000s.

She said: "Were they actually doing it? I felt bad for those girls because [Hefner] was younger in those days, so he was harder to fool. So I'm like, 'Oh, my God, those poor girls are probably ruined.' "

She recalled seeing the sisters at a party years later, where they were "very quiet".

She added: "I just felt so bad. I was like, 'Look at them; they just look ruined from this place.' And that's why I promised myself I wouldn't stay [at the Playboy Mansion] very long."

Crystal, 40, gave a shocking interview about her life in the Playboy Mansion last month, accusing her late husband of sexual abuse.

Asked if she believes she was raped, she said on the Lisa Guerrero Unleashed podcast: "I do believe that I did whatever he wanted me to do. And if that involved sex, then I just did what he wanted me to do.

"There were times that were really uncomfortable for me in the bedroom. In the bedroom things would happen that ended up just not being OK."

She also recalled how Hefner allegedly tried to "shove" Karissa and Kristina onto one another to "get them to engage with each other sexually."

She added: "That is incest. That is disgusting. I didn't want them to have to do something like that with each other. So that was very, very hard."