Britney Spears has finished her nearly month-long rehab stint in rehab and has checked out of Promises in Malibu.

The pop princess left the treatment facility late yesterday “after successfully completing their program,” said her manager, Larry Rudolph, in a statement released by Jive Records. As TMZ reported yesterday, Spears has made an amazing turnaround since she entered Promises on February 22. What’s more, as we reported, she and Kevin Federline have agreed share custody of their sons temporarily as they finalize their divorce.

Meanwhile, things aren’t quite so amazing for K-Fed. As Page Six reports, the one-time rapper has had to cancel his birthday party in Hollywood tonight at Eleven nightclub, possibly because party sponsors bailed. Federline had reportedly tried to get a glossy magazine to cover the bash – for $25,000 – but none of them bit. According to his rep, Kevin “decided that one party was enough.”