After Cowell fired her as a judge on his TV talent show Britain's Got Talent in 2009 - after just three days - Brook decided to take a break in Los Angeles, and landed her first major Hollywood movie role.
She was spotted dining out in Santa Monica by the film's director Alexandre Aja.
Brook auditioned for his flesh-eating fish movie and landed the role - and then texted Cowell.
She says, "I wrote, 'I hear you found a great new singer named Susan Boyle. Good luck with that. I’m in Arizona getting eaten by a fish."
But Brook insists she has no hard feelings about her former boss.
She tells the Los Angeles Times, "I’ve gotten to a point in this business where I’m resilient to the highs and lows. If I could make being fired by Simon Cowell into a positive, I must be doing something right."