Maks Chmerkovskiy Says He's 'Not OK' After Taking Son to School: 'Tearing Up in the Parking Lot'

Maks Chmerkovskiy is feeling emotional as his son starts his first day of school.

On Tuesday, Chmerkovskiy and Peta Murgatroyd's 5-year-old son Shai headed off to kindergarten, leaving the Dancing with the Stars pro, 42, "tearing up in the parking lot."

Chmerkovskiy posted an adorable picture on Instagram of Shai smiling on his big day, holding up an all-about-me sign that indicated the name of his teacher, his age, the date and what he wants to be when he grows up.

"First day of kindergarten! Shai's is excited, @petamurgatroyd is devastated, pops (me) is not ok. The whole 'blink and he's an adult' thing is too real. Tearing up in the parking lot….again 😭😭😭," he captioned the cute set of snaps.

Shortly after, Chmerkovskiy shared a video from school drop-off, during which the professional dancer couldn't get over how big his little boy had gotten.

"Why is he so big? Maybe if I sit down he won't appear so big. Why are you so adult?" Chmerkovskiy asks as he flips around the camera.

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"Best job I've ever had," he captioned the video.

Murgatroyd shared on her Instagram Story Monday night that she would be missing Shai's first day of school as she was leaving for New York City.

"Missing Shai's first day of school tomorrow was a tough pill to swallow and a 'moment' for me," she admitted. "I haven't missed anything, ever. And this is a big milestone. So I'm sad and just feeling blah. Lots of tears and kisses tonight."

Last month, Murgatroyd, 36, spoke with PEOPLE at the premiere of The Great Wolf Pack: A Call to Adventure in Garden Grove, California, about what's next in her IVF journey.

The professional dancer had earlier revealed on Instagram that her most recent embryo transfer was unsuccessful.

"I'm feeling great today. I'm feeling really positive," Murgatroyd told PEOPLE on the carpet, "It's only been six days, but yeah, it has been a rough couple of days. But today I'm feeling great, spending time with my family. I just love to be grateful for it."

As for her next step, the star said she planned to "just to take a little break for a couple of months" before starting the process over again.