Katharine McPhee teased by future stepdaughter Sara Foster, who's older than she is

What do you do when your future stepmother is younger than you are?

Poke fun at her swimsuit choices, apparently.

That's what Sara Foster was doing on Instagram on the last day of 2018, captioning a photo of herself and Katharine McPhee: "When your mom refuses to dress age appropriately."


McPhee, 34, is engaged to Sara's dad, the musician David Foster, 69.

Sara Foster is 37.

McPhee had already been heating up social media this holiday season. The recently engaged star showed off her bikini body in a yellow swimsuit while relaxing with a matching flower in her hair in Hawaii last week.

"Mele kalikimaka is hawaii's way..." McPhee captioned the photo from her vacation with Foster.

McPhee and Foster have known each other for more than a decade. McPhee, then 22, first met Foster on the set of "American Idol" in 2006 when he was a guest mentor for contestants on the show.

“She didn’t catch my eye on the first day because I was so busy trying to do my job,” Foster told People magazine. "But, the reality is that in the last 12 years I’ve always had a connection with her.”

But wait, it gets even weirder! Foster then played piano at McPhee's 2008 wedding to Nick Cokas.

McPhee has taken the attention to their age difference in stride, posting this photoshopped poster for Thanksgiving.