Katharine McPhee Shares Throwback Pregnancy Photo as She Gets Ready for Son Rennie's 4th Birthday: 'Where Does the Time Go?'

Katharine McPhee Foster is getting ready for her son's birthday by taking a minute to look back.

On Friday, Feb. 21, the actress, 40, shared a throwback photo on her Instagram Stories as she got ready to celebrate her son Rennie's 4th birthday. In the snap, McPhee Foster appears topless, baring her pregnant belly.

Across the photo, McPhee Foster, who shares Rennie with husband David Foster, wrote, "Night before I gave birth! 🤩."

The star also shared another sentimental message on her Instagram Story alongside a video of Rennie coloring, writing, "Last day of 3 💔💔 where does the time go? It hurts! But also he's a knucklehead 😂🤩."

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Related: Katharine McPhee Jokes David Foster Is ‘Devastated’ After Son Rennie, 3, ‘Lost Interest’ in Playing the Drums (Exclusive)

Earlier this week, McPhee Foster shared a Reel on her Instagram of her son Rennie learning how to ski. In the video, the toddler can be seen racing down the slopes, holding hands with his mom. "He’s a natural 🏂," she wrote.

Last year, McPhee Foster shared that her son was starting to take an interest in playing the drums. However, she later spoke with PEOPLE on the red carpet for the 58th Annual Country Music Association Awards and shared that her son is no longer interested — much to her husband David Foster's disappointment.

"If you’ve noticed, we’ve kind of stopped posting so many videos. He’s not as interested as he was," McPhee Foster lamented. "We were never making him play. We were never demanding that he play. But he’s just sort of lost interest."

"He’s very much into me. Obviously, I'll take it ‘cause I love it, but he’s really into everything Mommy," she continued. "Just being active and running and playing with his toys and things like that, so he’s just taken a little hiatus. My husband’s devastated about it."

Rennie made headlines last year when a video of him drumming at one of his dad's Washington D.C. shows went viral. Despite the toddler being unmic'ed and just banging along while Foster's drummer JR Robinson was playing, it was obvious Rennie was an incredibly skilled prodigy.

"It was pretty amazing," Foster, 75, told PEOPLE at the time. "He's studied our drummer JR Robinson, who's incredible, for the last year and a half and he's figured it out on his own."

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