Britney Spears is officially divorced - but at a stiff price.

The Star Magazine reports the singer's divorce from Kevin Federline will cost her $13 million, including $25,000 a month in child support for each of the couple's two sons until they reach 18. He also gets custody of the boys four days a week.

Kevin Federline gets to keep all the gifts Britney Spears bought him during their two-year marriage - but is forbidden from writing a tell-all book about their union.

He reportedly encouraged Britney to remain in a treatment center by telling her they would reconcile after she got out.