Reese Witherspoon and Ryan Phillippe reunited to give their 18-year-old son Deacon Phillippe a graduation experience he won't forget. Photo / Deacon Phillippe

Reese Witherspoon reunited with ex-husband and Cruel Intentions co-star Ryan Phillippe to celebrate their son's high school graduation in DIY-style.

Deacon Reese Phillippe, 18, who was homeschooled, graduated high school in June. But the proud parents were determined to pull out all the stops and give Deacon a home graduation to remember.

In a video posted to Instagram, Deacon walks out to the classic "Pomp and Circumstance", draped in a bright orange gown and a matching cap, completing the look with black sunglasses.

Phillippe, dressed as a principal, and two friends stood at the head of the backyard pool in ceremonial robes waiting to hand Deacon his high school diploma.

With a big cheer from friends and family gathered behind the camera, Deacon shakes their hands and accepts his certificate – tassel moved to the other side — and lets out a great big "Yeah!" before throwing his cap in the air.

Witherspoon proudly watched her son graduate — and then fished the cap out of the pool.

She posted her own tribute to Deacon on Instagram congratulating him on his graduation.

"So proud of the thoughtful, talented, kind & generous young man you have become," the post read. "You light up our hearts and make us proud everyday."

The certified "valedriptorian" shared his own pictures to Instagram as well, including a close-up of his diploma, signed by his parents.

Deacon is the second child of Witherspoon and Phillippe, who also have a 22-year-old daughter together, Ava, pursuing a career in both modelling and acting.

Despite their split in 2006, Witherspoon and Phillippe appear to have maintained a friendly relationship.

Witherspoon is currently married to Hollywood agent Jim Toth, with whom she shares her nine-year-old son Tennessee.