The Waitress star attended the annual fashion soiree at the Metropolitan Museum of Art in New York City on Monday with the 68-year-old musician, telling ET's Keltie Knight that she and her beau were having a "fun date night."
Fashion-wise, the 34-year-old Scorpion actress played on the 2018 theme, "Heavenly Bodies: Fashion and the Catholic Imagination," with a stunning, sheer blue Georges Chakra Couture Spring/Summer 2017 Collection gown, adorned with gold jewelry and a holy cross necklace.
"It's a lot of work I'm not gonna lie," McPhee said of the work that went into putting her ensemble together. "I'm just sort of the doll, but the hair and makeup and styling the last hour before you hit a carpet is kind of intense."
At the event, Foster -- who split with wife Yolanda Hadid in 2015 -- took a moment to greet his former stepdaughter, Bella Hadid.
Meanwhile, at this year's Met, McPhee is just across town in Manhattan from where she's been taking a starring turn in the Broadway musical, Waitress. Last month, the performer opened up to ET about taking to the stage.
“I feel like I have lived this part. Not to dive too far into my personal life, but I can tell this story in a really honest way," she shared. "I know good people can make big mistakes. I’ve made huge mistakes, and the issue is how do you learn to move forward and try to redeem yourself, and make better choices in the future?”
Check out the gallery below for more of this year's fabulous Met Gala styles.