Credit: Steve Granitz/WireImage

Destiny's child, indeed!

Fans worldwide were floored -- and thrilled -- when Beyonce unexpectedly announced her pregnancy at Sunday's MTV Video Music Awards in L.A. Clad in a loose, red Lanvin gown, the singer, 29, first rubbed her belly and told photographers the big news outside the show venue; her rep then confirmed it to Us Weekly.

Later, after a joyous onstage performance of "Love on Top," Beyonce unbuttoned her sequined D&G jacket and playfully rubbed her tiny bump once again. In the audience, dad-to-be Jay-Z (her hubby of three years) beamed as pal Kanye West congratulated him.

"She's close to four months along," an insider close to the music supercouple tells Us of the normally private star. "She wasn't going to announce it but she is so excited she couldn't hold it in."

And the first-time dad Jay-Z (real name: Shawn Carter), 41, is just as pumped. "Jay is ecstatic and over the moon," the insider says. "He really wanted this so badly."

So far, the Grammy-winning duo haven't found out the gender of their first child -- and are keeping other details close to the vest. "They barely told anyone...They kept it really secret until they were sure," the pal explains, "and now she simply couldn't wait to tell the world!"

The baby news does complicate their professional lives, though -- shooting for Beyonce's high-profile film project A Star Is Born has been delayed, while Jay-Z has a big-time tour to deal with.

"They will have to make adjustments," admits the source, "but this is worth it!"