Britney Spears was all smiles for an outing with her boyfriend, David Lucado, and her dog, Hannah, yesterday in LA. She showed off her legs in a pair of cutoff denim shorts after changing from her workout gear earlier in the day. Britney has been hard at work preparing to unveil a possible secret performance that she has been teasing on her Twitter account. Last week she wrote, "Taking a quick break to say hi to all my tweeps. Rehearsing for something top secret happening next week." Along with her much-anticipated surprise in the works, it was announced yesterday that Britney will be performing live on Good Morning America on Sept. 17. The date of her GMA performance conveniently falls on the same day that the countdown on her website expires. The big reveal could have something to do with the rumors surrounding Britney's stint at Planet Hollywood in Las Vegas, but we will just have to wait and see!