The American Idol alum, 33, and music producer, 68, were spotted on Dec. 26 strolling around Paris, France, stopping for hugs and kisses in the "City of Love."
McPhee wore navy leggings, pink Nike sneakers, a black knit hat and chic sunglasses, while Foster rocked blue jeans, gray sneakers and green shades with one lens missing.
The couple first sparked romance rumors in May after being spotted cuddling up in Malibu, and have been spotted together at a number of events since.
A source told Us Weekly in November, “When Kat talks about David, her face lights up. She’s really so happy. They’re actually so sweet together. … The age difference might seem substantial to some, but they are really cute together and it makes sense.”
However, McPhee has kept quiet about the relationship, declining to confirm her relationship with Foster in a recent Health magazine cover story. “We’re very close friends, and we’ve been friends for a long time. I’m really, really fond of him, and I think he’s an incredible person.”
The American Idol season 5 runner-up previously dated Smash co-star Elyes Gabel, ending their relationship after two years in July 2016.
"It was an amicable split. They're still friends and work together almost everyday. They still love each other but just couldn't make things work," a source told Just Jared at the time.
McPhee and Gabel were first linked in 2014 after they stole a kiss on the set of their show, Scorpion. Things were official shortly thereafter.
The couple began dating after McPhee filed from divorce from her ex-husband Nick Cokas, in March of 2014 after splitting the year before.