A rep for the 68-year-old musician confirmed to ET on Tuesday that he's engaged to 34-year-old McPhee, after proposing to the singer and actress while they were vacationing in Europe. The upcoming marriage will mark Foster's fifth, and the second one for McPhee.
According to our source, Foster and McPhee enjoy a tight bond, and, tellingly, he's adjusted his busy work schedule to make time for her. The two have actually known each other for over a decade -- McPhee told Health magazine last November that Foster produced her first single, and that she's known him since she was 21.
"From the very beginning, he and Katharine had a special bond," the source says. "David took a lot of time off work to spend with Katharine. He is dedicated to his work, but he didn't want to miss out on any time with Katharine, so it was worth it for him.”
Their relationship was apparently further solidified after McPhee bonded with his children. Foster has eight children from previous relationships -- Sara, Erin, Amy, Gary, Jordan, Allison, Greg and Tim -- and our source says they very much approve of McPhee.
"David's children are what is most important to him in his life, so the approval of his children was key to making this a lifetime choice," the source says. "Katharine became friends with his kids and they are thrilled she is part of his life. She immediately hit it off with his children, and that is what sealed the deal for him. Their engagement was a beautiful thing. Everyone is thrilled for them and can't wait to celebrate.”
"There is no question that David is a hopeless romantic, but we thought David would never marry again after the difficult time he had at the end of his marriage to Yolanda," the source notes. "Four times is a lot of weddings and he wasn't planning on having more kids.”
"He and Yolanda went through an incredibly bumpy time and he threw himself into his work," the source continues. "He seemed unhappy then. Soon after he started dating Katharine, he did a complete turn around and actually is quite starry-eyed. He fell in love immediately. It was as if it was meant to be.”
ET spoke with Foster at his home in March, and he talked about dating someone who approves of his kids.
"Well, you can't come between a man and his children," he said. "So, if whoever you're with gets along with your children, it's just such a bonus."
ET also spoke to the couple at the Met Gala in May, when they talked about their "fun date night." Watch below: