Brian Austin Green and Megan Fox’s kids are all grown up!

Noah, 12, Bodhi, 11, and Journey, 9, made a rare social media appearance in the latest Instagram post from Sharna Burgess, who marked their half-brother Zane’s first day of pre-K on Tuesday, Sept. 2. Burgess, 40, and Green, 52, are engaged and welcomed Zane in June 2022. (Green is also dad to Kassius Lijah, 23, whom he shares with ex-girlfriend Vanessa Marcil.)

The new reel begins with Zane holding up a sign celebrating his first day of school while his older siblings encourage him. As he breaks into laughter, Burgess switches to a slideshow, which includes a picture of Zane standing between Noah, Bodhi and Journey. The reel ends with Burgess driving, on the verge of tears after dropping Zane off at school.

The Dancing with the Stars pro began her caption by explaining how she makes videos for him of “milestone moments” she hopes to share with him when he grows up.

“Its wild watching him grow into this life and this body but still remember details of another time,” Burgess wrote in part. “I know one day he will forget those things so I always try to document it all for him.”

Zane “felt a little bigger, a little more grown, and a little less baby,” she continued. “I am not well. And yet I couldn’t be more proud.”

Burgess also gave props to Noah, Bodhi and Journey for their support.

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“His siblings hyped him up this morning as you can hear, and we all went to support his first morning drop off,” she wrote. “My blended tribe is my everything. We are so lucky.”

Fox, 39, and Green were married from 2010 to 2021. Since their split, Fox has also welcomed a new addition. In March, she and her ex-boyfriend Machine Gun Kelly welcomed a daughter, with whom Zane has already developed a connection.

“Of course he’s met her — that’s his baby sister,” Burgess told PEOPLE in June. “They’re deeply in love. She is the absolute cutest thing, and it’s really beautiful.”

Burgess also described Zane’s older siblings as “built-in babysitters,” adding that, “The age gap actually works really well. We’re thrilled.”

The Beverly Hills, 90210 star also continues to support Fox, Burgess told PEOPLE, because he knows “it’s the right thing to do, she deserves it, and it doesn’t matter what anyone else thinks.”

“It’s because we all support each other,” Burgess continued. “[Fox] is the mother of my bonus babies. She is the mother of three kids that I absolutely love, and she’s a part of them. And so absolutely the only way forward is to support.”