Pregnant Serena Williams hangs out with Mariah Carey and her twins after concert -- see the pic!

Serena Williams is very pregnant and on the move.

On Thursday night, the 35-year-old tennis pro showed up to see Mariah Carey perform in Fort Lauderdale, Florida, and greeted the singer backstage, along with her 6-year-old twins, Monroe and Moroccan.

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"With the beautiful @serenawilliams backstage tonight," Carey captioned a pic of herself and her kids posing with Williams.

Carey opened for Lionel Richie at the concert, and Williams -- who went to the show with her mother, Oracene Price -- was sure to Snapchat her love for their performances. The mom-to-be thoroughly enjoyed seeing the 47-year-old diva crooning "We Belong Together," and had an all-out singalong when Richie hit the stage.

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Williams has been keeping busy in lead-up to the birth of her first child with fiance Alexis Ohanian. Last week, her friends threw her a '50s-themed baby shower, and they got all dressed up for the occasion.