The British model and actress has been at the Cannes Film Festival with the comedian to promote Keith Lemon: The Film.
Brook stated that even though the film was likely to be "disgusting", she had enough free time to agree to it.
"I read the script and there wasn't much work coming in at the time, so I was available," she is quoted as saying by The Sun.
"I thought, 'Yeah, this is offensive and quite disgusting and, yeah, I'm probably going to get abused for it by Keith the whole way through - but why don't I just go for it and have a good time?'"
Brook added that she is nervous about her family watching the film, saying: "I think they will be a little shocked.
"I've done girl-on-girl in films, but that was tame in comparison to this - what Keith does to me in this film is far more offensive."
Brook recently topped a list to be voted the 'Most Desirable Celebrity Legs'.