Britney Spears  blindsided by a new bombshell – her ex-husband Kevin Federline’s girlfriend is telling pals she is pregnant!

Pro volleyball player Victoria Prince said she found out in mid-October that she’s expecting K-Fed’s fifth child, and friends fear the surprising baby news could send the emotionally fragile Britney back off the rails.

Despite having a string of relationships since her divorce from Federline, Britney has long hoped for a reconciliation, say those close to her.

"Britney never wanted Kevin to have another child unless it was with her," revealed a source. "She desperately wants to have a baby girl, and she had hoped Kevin would be the dad."

Federline, 31, already has four children – daughter Kori, 7, and son Kaleb, 5, with former flame Shar Jackson, and sons Sean, 4, and Jayden, 3, with Britney.

Victoria has been living with him since she quit working last spring. The leggy 26-year-old suspected she was pregnant after the two spent a weekend in Las Vegas in mid-October. After telling Kevin she thought there was a chance she was pregnant, he urged her to take a home pregnancy test to get a definitive answer, the insider divulged.

"The test was positive. She told Kevin that she was pregnant, but he didn’t seem happy to hear the news," the source revealed.

"Kevin wasn’t planning to have children with Victoria, and now he’s upset with her. Kevin says he loves her, but he told her that he didn’t want to get married again."

 "Even though Britney has tried to move on, she still has feelings for Kevin. The last thing she wants is Kevin having children with someone else."

For all the details pick up the new ENQUIRER