Katharine McPhee, 33, and David Foster, 68, have yet to confirm their suspected romance, but they had no problem sharing the stage for an intimate Christmas performance over the weekend.
The duo were joined by a slew of fellow musicians, including Keith Urban and Joe Walsh, at Oscar-winning songwriter Carole Bayer Sager's holiday bash in Los Angeles on Dec. 16.
With David on the piano, Katharine and Kenneth "Babyface" Edmonds belted out a rendition of "White Christmas" for the star-studded crowd.
The host made sure to share video of some of the other epic performances on Instagram!
Partygoer Kim Kardashian West also posted tons of footage from the night to her Instagram, including video of Katharine on stage with David and a clip where she's apparently reading lyrics from her cell phone for a solo performance of "Grown Up Christmas List."
Despite being photographed smooching while on a lunch date back in November, Katharine and David, who officially divorced Yolanda Hadid earlier this year, have stayed mum on the details of their relationship.
In September, David's daughter, Erin Foster, shared a photo of the alleged couple on social media with the joking caption, "excited about my new step mom."
"My dad is kind of a hopeless romantic," she told People mag the next month, "and Katharine's awesome. We really, really like her, and we've known her for a really long time. And, if he's happy, we're happy."
David actually met Katharine when she was a contestant on "American Idol" back in 2006, and they've seemingly remained friends since.