Sylvester Stallone's ex Brigitte Nielsen has insisted he couldn't have sexually assaulted a 16-year-old girl in Las Vegas in 1986 because she was with him the whole time.

The 'Rocky' star recently faced an allegation of historic sexual misconduct after it emerged an unnamed woman had claimed the Hollywood actor had ''intimidated'' her into having sex with him and his bodyguard Michael 'Mike' De Luca in a Las Vegas hotel room while he was filming movie 'Over the Top'.

But Brigitte - who married Sylvester in December 1985, but they split up 19 months later - claims the ''incident did not occur'' and that the pair were ''inseparable''.

The 54-year-old actress told TMZ: ''During the summer of 1986 we were newlyweds. I was inseparable with Sylvester when 'Over the Top' was being shot in Las Vegas. The story claims that at approximately 8:30 in the evening during the shoot of the movie the person claims she was in our suite at the Hilton Hotel.

''This incident did not occur. Most of the day, I would watch him film, then we'd have dinner and go to our room. No other person was in the room with him, but me.''

Brigitte - who isn't said to have spoken to Sylvester for around 30 years - believes it is ''impossible'' that the alleged incident could've ever happened.

She added: ''I can say for certain that it is impossible for this incident to have occurred.

''It's unbelievable that Sylvester and his family have to suffer through this over something that never happened.''

Sylvester has also denied the accusation.

His spokesperson Michelle Bega said: ''This is a ridiculous, categorically false story. No one was ever aware of this story until it was published today, including Mr. Stallone. At no time was Mr. Stallone ever contacted by authorities or anyone else regarding this matter. It never happened.''

According to a police report, which was filed at the time and recently obtained by the Daily Mail newspaper, the woman did not want to press charges because she was ''scared'', ''humiliated and ashamed'', and signed a ''no prosecution'' form.