Spears hits out at Federline in new song

Britney Spears has hit out at ex-husband Kevin Federline in the lyrics of a new song.

The singer accuses Federline of betraying her during their two-year marriage in the track 'Why Should I Be Sad'.

The couple divorced last year and have since been embroiled in a highly-publicised custody battle over sons Sean Preston, two, and one-year-old Jayden James. Spears recently lost her visiting rights after missing a court-ordered drugs test.

She refers to her ex's love of cars, money and women in the song, which she penned with hip-hop star Pharrell Williams.

In one line, she sings: "It just seemed that Vegas / Only brought the playa out of you."

A source told People: "The song is definitely about Britney and Kevin's relationship when they were married. Britney entertains the idea that she stayed home taking care of the kids while Kevin was out partying."