Katharine Foster is “very strong”, according to her new stepdaughter Erin Foster

Speaking to Us Weekly magazine, she said: “The truth is we really genuinely love Katharine. It takes a very strong, graceful person to come into a family as the fifth wife and have adult daughters who are older than her and do it in a way that really creates inclusion with the family, and she just does it effortlessly. She just makes it really easy for all of us to get along. So we’re very grateful for her.”

And when asked if she’s ready for another sibling if Katharine - who was previously known as Katharine McPhee - and David have a child of their own, Erin added: “Anything that makes them happy, I’m happy with.”

Katharine is now stepmother to five children, including Erin and her sisters Sara, 38, and Jordan, 32, whom David has with his ex-wife Rebecca Dyer, as well as Allison, 49, and Amy, 46, from previous relationships.

Meanwhile, the ‘American Idol’ alum recently said she is "enjoying" her new last name, although she isn’t used to hearing it just yet.

She said: "We've been away since we've been married, so [I'm not used to it], but I love it. I just love the ring of it, so I'm enjoying it.”

And although Katherine has become known by her maiden name, she didn't think about keeping it, because she's a "romantic" and always wanted to take her husband's surname.

She added: "I'm a romantic, I've always loved the idea of taking [his last name]. It's sort of a traditional thing that still exists in our society, but some people don't take their spouses last name anymore, so, I like the idea of it. I think it's romantic and it's a great last name."