Reese Witherspoon, Ex-Husband Ryan Phillippe Reunite For Son Deacon's 18th Birthday [Photos]

Reese Witherspoon and her ex-husband Ryan Phillippe just got together for a very special occasion.

Over the weekend, the former couple reunited to celebrate their son Deacon's 18th birthday.

Phillippe took to Instagram Saturday to share photos of him, Witherspoon and Deacon sitting together at a table and getting ready to indulge in some cake. The actor accompanied the family photos with a sweet message for his son.

"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," Phillippe wrote in the caption. "We are lucky to be your mom and dad. Love you, pup... (I’d say we did pretty good @reesewitherspoon)."

Deacon replied to his father's post, commenting, "Thanks, dad!! I love you."

The "Morning Show" star also commented on her ex-husband's post, echoing Phillippe's sentiments. "So proud of our boy," Witherspoon wrote. "I mean our ADULT son!"

Fans and followers of the actor wished Deacon a happy birthday in the comments section. Some praised the trio's "incredible genes," while others gushed over how Phillippe and Witherspoon have been co-parenting their children.

"What a testament to the love and support you’ve both provided. Beautiful family inside and out," Elex Michaelson wrote.

Witherspoon also shared a series of photos of her son on her own Instagram, writing, "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. Happy 18th birthday, Deacon! I love you to the moon around the sun and all the stars."

The two stars also share 22-year-old daughter Ava. Witherspoon is also mom to son Tennessee, 9, with husband Jim Toth, while Phillippe shares daughter Kai, 10, with Alexis Knapp.

Phillippe and Witherspoon met at her 21st birthday in March 1997. The former couple tied the knot in 1999 – the same year they starred in the R-rated cult teen film "Cruel Intentions" – and divorced in 2008.

Though their two children are now adults, Witherspoon and Phillippe are still reluctant to let Ava and Deacon watch the film due to its mature content. Last month, Phillippe told E! News that his thoughts on the matter haven't changed.

"You know, I haven't checked back in with them about it now that they're both of age," he told the outlet. "I don't know if it would be creepy for them, you know? In some ways, like if I were to think about watching my parents do some of the things that their parents do in that movie, it wouldn't be the most appetizing or appealing notion."