Jon Gosselin Wishes His Sextuplets a Happy 15th Birthday, Shares New Photos of Collin and Hannah

The sextuplets are 15!

In celebration of their special day on Friday, Jon Gosselin wished his six youngest children a happy birthday with a loving tribute on Instagram.

“Happy 15th Birthday Hannah, Collin, Alexis, Aaden, Joel and Leah!!!! Wow I can’t believe you are 15!!!” wrote Jon, 42.

“Time is flying by!!! I love you all very much. I wish you the best day ever and I hope you enjoy your birthday celebrations today and this weekend!!!” he continued. “Love always, Dad.”

For the birthday post, Jon shared three smiling photos of himself alongside both Hannah and Collin.

Although Kate Gosselin, who also shares 18-year-old twins Cara and Mady with ex-husband Jon, maintains full custody of their eight children, both Collin and Hannah live with Jon full-time.

In the fall, the Kate Plus 8 star’s children entered milestone years when they returned back to school: while twins Mady and Cara began their senior year, the sextuplets entered eighth grade.

Ahead of their first day back at school, Kate shared a photo of her kids in their school uniforms standing on the steps outside of their house.

“This was yesterday! Feels like school never ended…and they’re already back! #SeniorYear 😳😳 #EighthGrade #ProudMom ❤️” she captioned the smiling photo of Mady and Cara and Aaden, Alexis, Leah and Joel. Missing from the photo was son Collin, who was enrolled in a program away from home at the time to help him reach his full potential, and Hannah, who was with Jon.

Kate also shared a second image of the sweet note she wrote to her two eldest daughters as they began their last year of high school. “Happy 1st day of senior year! I love you sooo much! I’m so P.R.O.U.D. of you! Love, Mommy,” the note reads.

While each of her kids is beginning a different chapter, Kate is also entering a new season of life.

This summer, TLC audiences will see Kate return to TV for a series documenting her love life, Kate Plus Date.

“I started picturing myself sitting in a rocking chair, knitting, and words like ‘old maid’ and ‘spinster’ started to come to mind, and I realized that no, I don’t want that to be my fate,” she previously told PEOPLE of the series.