Ashlee Simpson has officially signed on to play the part of Roxie Hart in the London cast of Chicago. "Yes, it is true," the show's producer confirmed. "Ashlee Simpson is joining the cast of Chicago in London. We are very excited and are looking forward to gauging the London audience reaction." The reality TV show star began rehearsals today in NYC, and is slated to begin her run on stage in October. "Ashlee's a dancer, her background is in dance," says a source. "She wants to do live theater. This will put all of those critics to rest. She's always wanted to be on stage, but she got diverted when she started selling so many albums." Simpson is expected to make an offical announcement about her new gig sometime in the next few weeks.