"I’m pregnant!" revealed the 24 year-old pop star to another woman in the spa at Maui’s Four Seasons Hotel where Britney, Kevin and their baby son are staying.

But no one’s more surprised than Federline, who, sources tell Star, had no idea he was about to become a dad again. In fact, Kevin had only a slight jump on Brit’s fellow spa-goer — a source says he only got the news just days before from Brit in New Orleans just before he joined her on Feb. 27 for Mardi Gras.

Brit, 24, the sources tell Star, is near the end of her first trimester and found out in early January that she was expecting. Why wouldn’t she share the news with her husband then? Why wouldn’t he notice? One reason, sources say, is that the two had been having a particularly rocky time — and Brit was probably afraid Kevin wouldn’t want the baby.

As it turned out, sources tell Star, Britney was absolutely right in her concerns. A friend of Federline says that Kevin, 27, wasn’t very enthusiastic when he shared the latest baby news. "Kevin said, ‘Britney’s pregnant,’" the friend tells Star. "When I expressed surprise, Kevin said, ‘Yeah, it shocked the sh** out of me, too!’"

Finding out that she’s pregnant again may actually come as a relief to Britney. As previously reported, she was extremely frustrated at her inability to lose the 50 lbs. she put on during her first pregnancy. Plus, she was experiencing moodiness and junk-food cravings. In fact, a friend of Kevin tells Star that the mood swings had become an issue. "He’s totally stressed out," the friend says. "When I asked him what was wrong, he went off on Britney, saying: ‘One minute she’s nice and the next she’s cursing me out about nothing.’"