Wanna Feel Old?! Ashlee Simpson & Pete Wentz's Son Bronx Is 13!

They grow up so fast!

Ashlee Simpson and her ex-husband Pete Wentz are officially parents of a teenager! The exes’ son Bronx celebrated his 13th birthday over the weekend, and, of course, his momma couldn’t help gush about the milestone on her Instagram. The Pieces of Me singer posted an adorable black-and-white snapshot of herself cuddling the new teen on Sunday, reflecting:

“This is 13. Happy birthday Bronx. You are the coolest teenager. I LOVE YOU. I LOVE YOU. I LOVE YOU.”

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A post shared by Ashlee Simpson Ross (@ashleesimpsonross)

Adorbz!!

While the Fall Out Boy rocker has yet to make a public post in his kiddo’s honor, lots of Ashlee’s high-profile friends shared sweet messages about the big day, including Rachel Zoe, writing:

“OMG 13”

LOLz! Similarly, makeup artist Mary Phillips simply couldn’t get over how fast time flies, adding:

“Stop!!! Omg it feels like yesterday he was in your belly”

Even Simpson’s husband and Bronx’s stepdad Evan Ross got in on the action, commenting:

“BRONX HAPPY BIRTHDAY KING! LOVE U”

Cute!! Bronx is the oldest of his parents’ children. After Ashlee and Pete broke up in 2011, she went on to welcome 6-year-old Jagger Snow and 1-year-old Ziggy Blue with Evan. Pete also shares 7-year-old Saint Lazslo and 3-year-old Marvel Jane with his wife Meagan Camper. So, we’re sure having a teen feels like a whole new ballgame now!