From "Milkshake" to mommy!

A source tells the newest issue of Us Weekly, on stands now, that singer Kelis, 29, and her husband, rapper Nas, 35, are expecting their first child together.

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"It's all they are talking about. She is carrying hip-hop royalty!" says the insider, who adds Kelis -- currently in her first trimester -- already has a little bump. "They are so excited."

A rep for the singer had no comment.

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The couple tied the knot in a small ceremony in Atlanta in January 2005.