They love her confidence! Sara and Erin Foster are big fans of their father David Foster’s fiancée, Katharine McPhee, and aren’t afraid to show their adoration.

The sisters spoke exclusively to Us Weekly while promoting their partnership with CVS Pharmacy — in which they created a limited-edition T-shirt celebrating their groundbreaking Beauty Mark initiative — about the American Idol alum’s headline-making clapbacks.

“Oh, my God, Katharine is so funny,” Erin, 36, gushed to Us about McPhee, 34, and her ability to shut down haters who criticize her relationship with David, 69, who is 34 years her senior.

“Katharine holds her tongue a lot,” Sara, 37, added. “If I were her, I would be taking down trolls all day. I wouldn’t be able to star on Broadway because I’d be too busy taking down trolls. She’s really funny.”

Most recently, the Waitress star shared an epic throwback photo of herself revealing she has a long history with Duchess Meghan — and it seems it came as just a big surprise to Sara and Erin.

“That was crazy,” the 90210 alum told Us. “I had no idea that she was so close with Meghan Markle. This is all news to me. I feel way too distant from the royals.”

As for if the two are on board for their father and McPhee to potentially start a family together? “Listen, whatever they choose to do, we support,” Erin told Us. “So, if that’s what makes sense to them, we’re for it. We’re too busy living our own lives to try and worry about theirs.”

However, it isn’t all fun and games. Erin joked that during their recent family vacation in Hawaii, she had to keep her eyes closely on boyfriend Simon Tikhman.

“Imagine what it’s like to have a boyfriend on a vacation where your stepmom is hotter than you are and younger than you are,” she quipped of McPhee. “It’s, like, I have to make sure I had an eye on him.”

Erin added: “For Christmas, I got Katharine a beach cover up to cover up her body, that’s true. That is true.”

McPhee has been no stranger to slamming trolls who comment negative thoughts on her photos of herself with David since the pair got engaged in July 2018. Last month, she hit back at a commenter who referred to the music producer as her “geriatric love.”

“Oh i LOVE that demi lovato song,” McPhee replied, referring to Demi Lovato’s 2017 tune “Daddy Issues.”

The Sara & Erin x CVS “Sans Retouching” T-shirt is available for purchase on CVS.com with 100% of the sales supporting Girls Inc.

With reporting by Carly Sloane

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