David Foster’s Daughter Erin, 35, Calls Katharine McPhee, 34, 'Mommy' After Engagement News

David Foster and fiancee Katharine McPhee with Erin Foster (inset)
Dave Benett, Cindy Ord/Getty Images

The comedy writer ribbed her dad over his engagement to the much younger actress, who will be his fifth wife.

David Foster's daughter, Erin Foster, is poking fun at her dad over his recent engagement to Katharine McPhee.

The 68-year-old music icon and the 34-year-old Scorpion star revealed on Tuesday that they'd gotten engaged. A rep for David told ET that he'd popped the question over the weekend while they were vacationing in Europe.

On Tuesday, David shared a snapshot of himself and his new fiancée on a boat off the coast of Italy, which he captioned, simply, "Yup," along with a music note emoji -- thus reiterating Katharine's earlier tweet, in which she confirmed the engagement news by posting a diamond ring emoji.

In the comments below the pic, David's daughter Erin -- who is one year older than her dad's new fiancée -- responded to the photo, "Mommmyyy" along with three red heart emojis.

The comedy writer is best known for co-creating the VH1 mockumentary Barely Famous along with her sister, actress Sara Foster. Not missing a chance to rib her dad, Sara, 37, also got in on the joke, commenting, "Out of the country. What did I miss?"

David Foster/Instagram

David's engagement to the former American Idol star comes after four previous marriages. Foster was previously married to B.J. Cook, Rebecca Dyer -- with whom he welcomed Erin, Sara and daughter Jordan -- Linda Thompson and Yolanda Hadid, whom he split with in December 2015. All together he has eight children from his previous relationships.

This will also be the second marriage for Katharine, who was previously married to Nick Cokas from 2008 to 2016.

Foster and McPhee were first linked together last May, and by December of 2017, they couldn't seem to keep their hands off each other during a PDA-packed trip to Paris, France.

When ET caught up with Foster at his home in March, he explained what it's like to date 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."