David Foster, Katharine McPhee 'are perfect for each other,' record producer's daughter Amy says

From left to right: David Foster, his daughter Amy Foster, and his fiancee Katharine McPhee. (REUTERS, Getty)

David Foster’s daughter, Amy, is telling “haters” to keep quiet about her dad’s love life.

The record producer, 68, recently got engaged to 34-year-old actress and singer Katharine McPhee. It'll be the second and fifth marriages for the bride and groom, respectively.

The newly engaged couple received swift backlash after confirming the news in July — with many fans pointing out the age gap. McPhee was quick to shut down critics, tweeting on July 6 they should be “worrying more about registering to vote and midterm elections than who’s marrying me.”

Now Foster’s 44-year-old daughter with his first wife, B.J. Cook, is also stepping in to defend the couple.

“I know that some people have been hating on that relationship,” Amy told US Weekly on Saturday. “All I can tell you is it absolutely works when you see them together.”

The songwriter continued, “It’s love. The haters [can] shut the f--k up because they are perfect for each other.”

Amy only had praise for her future stepmother, who she described being “so close with.”

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“She’s amazing and funny, fun, smart, elegant, timeless, beautiful, talented. I can’t say enough about her,” Amy added.

She's not the only daughter to stick up for the relationship.

In early July, Foster’s 35-year-old daughter, Erin, from his marriage to second wife Rebecca Dyer, called McPhee "mommmyy" in a comment on her father's Instagram post.

Her sister, Sara, jokingly added, "Out of the country. What did I miss?"

Erin has nothing but praise for the former “American Idol” star.

“She’s amazing,” she told People in October. “I really like her. She’s awesome. My dad is kind of a hopeless romantic, and Katherine’s awesome. We really, really like her, and we’ve known her for a really long time. And if he’s happy, we’re happy.”

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David Foster's third wife, Linda Thompson, also shared her support for the happy couple.

“I think the only thing that’s a real deterrent, I think, is the age difference,” she told Us Weekly earlier this month. “But I think life doesn’t have any guarantees anyway. If you find someone you love, go for it, you know?”

Thompson added, “[McPhee is] a lovely person. She’s beautiful and she’s talented, and they have that musicality in common, so that goes a long way.”

Fox News' Morgan M. Evans contributed to this report.