LATEST: Troubled pop star Britney Spears has appeared on her favourite U.S. sitcom HOW I MET YOUR MOTHER. The Toxic hitmaker made a cameo appearance on the show - playing a secretary opposite Neil Patrick Harris - which aired on Monday night (24Mar08). Spears, 26, is a huge fan of the show, and deemed a guest role in the series a perfect assignment at this juncture of her turbulent career. And U.S. TV critics have been complimentary of her performance, describing her appearance as "fresh-faced and relaxed".