Reese Witherspoon and Ryan Phillippe reunited for a special occasion: their son Deacon's 18th birthday.

Deacon, who turned 18 on Saturday, shared a slideshow of photos on Instagram for his big day, including one of him sitting between his mom and dad with a big cake on the table in front of them.

The teen's parents also shared their own tributes for him.

"Happy 18th birthday to our gorgeous, smart, talented, and caring son. You are a true light in this world and are so loved by all who know you. We are lucky to be your mom and dad. Love you, pup," Phillippe, 47, wrote on Instagram. He added in parentheses, "I’d say we did pretty good @reesewitherspoon."

Witherspoon, 45, got equally sentimental in her Instagram post.

"How did this happen?!! @deaconphillippe is 18?!! One day he was trading Pokémon cards, singing Bruno Mars songs, and playing American Ninja Warrior in the backyard. The next day, he is taller than me, cooking the family steaks on the grill and making his own music with his best friends," she wrote.

"My heart is bursting with pride about the young man he is becoming," the Oscar winner continued. "Happy 18th Birthday Deacon! I love you to the moon around the sun and all the stars."

Witherspoon and Phillippe married in 1999, the same year "Cruel Intentions," the movie they starred in together, premiered. In addition to Deacon, the former couple -- who divorced in 2007 -- also share a daughter, 21-year-old Ava Phillippe.

Witherspoon also has a son Tennessee Toth, 9, with husband Jim Toth while Phillippe had a daughter Kai, 10, with ex Alexis Knapp.