Simpson and Contostavlos recently met through mutual friends and have shared a number of dates. Yesterday, Ward said she was three months' pregnant with the Newcastle United footballer's second child and branded the X Factor judge a "homewrecker".
Today, Ward told The Sun that she and Simpson had watched the footage that was leaked online by Contostavlos's ex Justin Edwards.
"Danny showed me the video on his phone as we sat on the sofa. I think one of the football lads sent it him," Ward said.
"We watched it together but it didn't turn us on or anything - it was rubbish. I remember Dan laughing his head off."
Ward added: "He said, 'Oh my God, she needs to work on her tekkers (technique)'. It's ironic to think that he didn't think she was very good in the bedroom - and now he's with her."
The 25-year-old, who is also mother to Simpson's 18-month-old daughter Skye, claimed that she slept with her ex as recently as November 5.
She said: "It's so upsetting as we only had sex with each other on Bonfire Night after having a lovely night at a firework display with Skye.
"To think he slept with me while he was chasing after Tulisa - it's disgusting."
Yesterday, Contostavlos slammed Ward's claims, calling her "a psychotic obsessed nutta (sic)" on Twitter.
The N-Dubz singer's lawyers also released a statement denying allegations that she started a relationship with Simpson while he was with Ward, or that she knew Ward was pregnant with the former couple's second child.
> Tulisa dating Newcastle United footballer Danny Simpson?
> Tulisa unveils 'Live Your Life' lyric video - watch
> N-Dubz should sign to my label for comeback, says Fazer