AceShowbiz -

Kevin Federline's brother Christopher made a bizarre claim that Britney Spears' eldest son Sean Preston is his son. Christopher has launched a legal action against Britney who allegedly threatened to reveal the secret to public.

Christopher is seeking a restraining order against Britney, calling her a "maniac" who stole his credit card and spent thousands of dollars on Archie and Betty Boop comics as well as Mad magazines. He also claimed that Britney tried to blackmail him when he confronted her with the theft. She was even said mocking the size of his manhood.

"She is out-of-control and a maniac. (She) went to Kevin's house to pick up Sean Preston and Jayden James, and (my) wallet was on Kevin's coffee table when Britney opened it up and stole (my) Capital One credit card," Christopher said in his lawsuit, which was obtained by Radar Online.

Christopher continued, "Britney laughed at me (and) told me my brother Kevin ruined her life. Britney made fun of me and told me I have a small penis. She also blackmailed me and told me if I tell the police that she stole my credit card, that she will tell the world I'm the true father of Sean Preston, not Kevin. I do confess I slept with Britney, and I am the true father, but the public does not need to know."

Sean was conceived when Britney and Kevin were married. Christopher claimed he had a fling with his sister in law but realized that it was a mistake. "He says he always felt bad about it and kept it to himself because he didn't want Alisha, his wife at the time, to find out," a source said.