Kevin Federline by Jamie McCarthy/WireImage.com Kevin Federline by Jamie McCarthy/WireImage.com

Britney Spears' assistant and cousin, Alli Sims, was subpoenaed on Sunday to make a statement "in connection with the Britney Spears/Kevin Federline issue," K-Fed's attorney tells the Associated Press. Sims was flagged as a person "believed to have relevant information," says the lawyer, who declined to discuss the specifics at hand.

Subpoenaing Sims was not a matter to be taken lightly. According to the New York Daily News, Federline's peeps retained "security expert" Aaron Cohen (formerly of the Israeli army!) to track down and serve Sims at an early-am Hollywood Hills bash. "Kevin is very serious about the case," his lawyer tells TV's Extra. "[We] believe [Alli] has been around the environment where the kids are... and [is a] witness to many things." Including countless fashion don'ts.