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.
"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.
Check out the epic themed soiree: