The rapper, who reportedly took part in an intervention to persuade the troubled superstar to seek help for unspecified problems, paid the pop star a visit at the Promises treatment center in Malibu, California.

Federline is reportedly looking after the couple's two sons while his estranged wife is seeking help.

A source close to the couple tells People magazine, "He cares a lot about her."

The insider claims Federline spent 90 minutes at Promises.

A friend of Federline's adds, "Britney scared everyone pretty bad. Kevin is worried that's for sure. Kevin just wants her to be OK."