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Sexy mama-to-be!

Christina Aguilera is expecting a baby girl with fiancé Matthew Rutler, and the singer decided to celebrate the summer solstice by posting an Instagram snap of her growing bump!

"Happy 1st Day of Summer! Keep those lips hydrated! @eosproducts #mint #summersolstice," she captioned the photo of herself in a blue tank applying lip balm.

Product placement much?!

The blonde beauty is taking a hiatus from judging The Voice while she prepares to welcome her second child, so Gwen Stefani is stepping in and taking her place temporarily.

"I’m really excited to meet our baby girl...This has been a very easy and enjoyable pregnancy," she told People earlier this month.

Let's hope son Max is ready for a little sister!