It turns out on a mountain in Anacapri, Italy.
"We totally approve!" she shared. "He said it was one or the other, And in the end he spared me".
The couple is now on vacation in Europe, which is where the proposal is believed to have taken place.
Mcphee and Foster were first romantically linked back in September of previous year, when his daughter Erin Foster posted a picture of the two together in L.A. Adding the age difference between 68-year-old David and 34-year-old Katharine works for them despite seeming odd to many.
His actress daughter, Sara Foster, has also has been open about her father's relationship with McPhee, dropping hints about their romance before the couple officially acknowledged the dating rumours. "If we ever thought that anyone was in something for the wrong reasons, we would be very vocal about it".
Katharine was married to Nick Cokas from 2008 to 2016. David was formerly married to Yolanda Hadid, star of "Real Housewives of Beverly Hills".