Among the carousel of shots is one image of McPhee and Foster, 72, with their son Rennie, whose face can be partially seen looking down at a piano. The Smash alum has previously hidden her little one's face entirely from view when sharing photos of him on social media.
In the caption of her post, McPhee paid tribute to Foster, whom she described as being the man "who loves me like I could have only dreamed of & who made me complete in life by making me a mommy."
"I love our little family. I love our big family," McPhee continued. "You have NEVER complained over how your life is slightly different now. Well… you only complain that you can't stay up late watching TV in bed but how can I blame you -that's your favorite thing."
Added the star, "You've only made bringing Rennie into the world an absolute joy for me. To many more adventures baby! 🎊I love you to the moon and back."
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Katherine McPhee/Instagram Katharine McPhee and son Rennie
McPhee and Foster welcomed their son in February 2021.
"Katharine McPhee and David Foster have welcomed a healthy baby boy," a rep for the couple told PEOPLE at the time. "Mom, Dad and son are all doing wonderfully."
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RELATED VIDEO: It's a Boy! Katharine McPhee and Husband David Foster Welcome a Son
Back in April, McPhee and Foster chatted with Entertainment Tonight at Clive Davis's 90th birthday celebration, where they raved about being new parents together.
"It's great. It's the best," the star said, while her husband added, "She's a fantastic mother. An amazing mother, and we are having the best time."
McPhee told ET she was "having so much fun" as a mom, despite some sleepless nights.
"I love it, absolutely. I mean, last night was a little rough, the time ... he was up and then you know, when you're traveling with the kid, you have your moments where you get over-tired and frustrated," she explained. "But it's just so precious because it's just a moment in time that is not going to last forever, so, in my perspective I just cherish."