The "American Idol" alum posted a series of Instagram Stories from Italy with her new music producer husband.
She also changed her Instagram name (though not her handle) to "Katharine Foster."
McPhee, 35, married Foster, 69, in London last week, a source previously confirmed to Fox News.
"Her special day finally came and it was everything she could have imagined it would be. It was a long time coming and this one just felt right to Katharine," the source gushed. "Regardless of what other people have said about her and David’s relationship – it was more than a decade in the making and she’s happy."
“Exactly 13 years ago today my very first single, Somewhere Over The Rainbow, was released right after Idol. Today… I’m marrying the man who produced it. Life is full of beautiful coincidences, isn’t it? Thank you for taking me over the rainbow, David,” McPhee wrote on Instagram Friday.
After the wedding, Foster posted a photo of McPhee in the car, writing, "I'm in the best seat ever!"
McPhee is Foster's fourth wife. His most recent bride was "Real Housewives of Beverly Hills" star Yolanda Hadid, from whom he separated in 2015 and divorced in 2017.
Foster and McPhee were first rumored to be a couple in fall 2017. They confirmed their romance in May 2018 and got engaged that July. "He did it at the top of this mountain in Anacapri," McPhee revealed on Instagram. "Totally dark, only stars." She added jokingly, "Thankfully, he didn't push me off the cliff. He said it was one or the other. And in the end he spared me."
Fox News' Julius Young and Mariah Haas contributed to this report.