McPhee, 34, rocked a sheer blue dress by Georges Chakra Couture and accented her look with bold jewelry, including a golden cross necklace. Meanwhile, Foster, 68, looked dapper in a black suit and tie.
They later changed into different glamorous outfits for a star-studded afterparty!
While posing for photos, the Waitress Broadway star told ET that they were enjoying their "fun date night".
So that's that!
As Radar readers know, Foster and McPhee sparked dating rumors when they were spotted together at the Grammys Museum Gala on September 10, 2017.
At the time, Foster's daughter Erin even joked on Instagram: "excited about my new step mom" as she shared a video of Foster and McPhee.
The love birds have been spotted out on steamy PDA-filled dates many times ever since, despite skeptical fans believing it was just a casual fling.
Does their Met Gala debut mean Katharine McPhee and David Foster are getting serious? Let us know your thoughts in the comments below.
We pay for juicy info! Do you have a story for RadarOnline.com? Email us at firstname.lastname@example.org, or call us at (866) ON-RADAR (667-2327) any time, day or night.