The Laguna Beach guys and gals commemorated a bunch of teenage milestones back in the day -- spring break, prom and graduation, to name a few. And more than a decade later, the OG MTV crew is continuing to mark important events together -- and this past weekend, Stephen Colletti, Trey Phillips and Dieter Schmitz reunited in the Big Apple for a special occasion.

"Human gem. Happy Birthday, Trey," Kristin Cavallari's former boyfriend/Lauren Conrad's best bud captioned the Instagram image above of the fashion designer from his 30th (YUP, the big 3-0!) celebration. Feels like yesterday Trey was organizing local runway shows with his close pals...

Fittingly, the guest of honor also shared a few snapshots from his own bash.

"What a beautiful day in New York to spend with old friends," the birthday boy added along with the snapshot above featuring the Three Musketeers. Little has changed from those unforgettable 2004 spring/summer days, that's for sure.

Check out more photographs from T's fun-filled weekend -- and offer your well wishes in the comments!