K-Fed to Make His Acting Debut on CSI FRIDAY AUGUST 25, 2006 10:00PM EST By Marisa Laudadio and Cynthia Wang Kevin Federline Photo by: Tammie Arroyo / AFF Kevin Federline, who made his nationally televised rap debut last Sunday at the Teen Choice Awards, is going for another first his debut as a TV actor on America's top-rated drama, CSI: Crime Scene Investigation, PEOPLE has learned exclusively. As Federline tells PEOPLE while on the set of the CBS show, "This is pretty much my first time acting. It's the first time I've actually had a speaking role." He adds that the offer came about quickly. "I was doing stuff for the Teen Choice Awards," he says, "and got the call while we were rehearsing and I pissed in my pants! I was excited right off the bat. It's the only show that I really, really watch." Federline, 28, started shooting his part in Los Angeles on Thursday night. He will play a menacing, arrogant teen who harasses investigators Nick Stokes (George Eads) and Warrick Brown (Gary Dourdan) on a job. The episode is tentatively scheduled to air in October. Fans of Federline and his wife, Britney Spears, 24, may remember their last foray into broadcast TV their own reality show, Britney & Kevin: Chaotic, which aired on UPN in 2005. But to take on CSI, Federline will rely on his instincts. "I just read the script," he says. "They told me they wanted it to be more of a natural thing that comes to me." Earlier in the day, the CSI producers announced another star addition to their lineup: Grammy Award-winning singer-songwriter John Mayer, who will make a cameo in the two-part season premiere, airing Sept. 21 and 28. In a scene set in a Las Vegas nightclub, Mayer will sing his single "Waiting On the World to Change" and "Slow Dancing in a Burning Room," both tracks off his third studio album, Continuum. Federline's first album, Playing with Fire, will drop in October, but he gave a glimpse of it at the Teen Choice Awards, where he performed the track "Lose Yourself." Afterward, he told PEOPLE, "I'm happy. I think I pulled if off pretty well. September 5, we're launching the video. There's a lot of good things going around here."