Katherine, 36, and David, 70, tied the knot in June 2019 after first meeting in 2006, when he mentored her on season 5 of American Idol.
This will Katherine’s first child, whereas David already has five daughters and has been married four times to B.J. Cook, Rebecca Dyer, Linda Thompson and Yolanda Hadid.
Speaking of her husband’s friendship with the Sussexes, Katherine previously said that Harry and David have developed a “father and son” type of relationship.
"My husband has a really, really beautiful relationship with Harry," Katharine told Access Hollywood in May.
"They're like, they're so cute. They're like father and son.
"We just stay in touch with them. But mostly, Meghan and I knew each other from childhood, but really Harry and my husband are friends. It's really nice," she said.
In another interview with British television program Good Morning Britain, Katherine again reflected on her high school days with the Duchess.
"I went to school with Meghan Markle, I was in middle school, she was in high school," she began.
The Smash star explained that, while in different years at school, they frequently crossed paths while performing in musicals at school.
"My sister was in her class, they were the same age… She was always lovely, always talented and always put together," she said.