The Legally Blonde star, 46, approved of his look, writing, “Love the 🌸🥰.”
Sister Ava Phillippe, 22, added, “Looking sharp!”
Ryan, 47, was on hand to celebrate the occasion. “Sending our sweet meat boi off 2 prom,” he wrote via Instagram Stories.
The former couple, who finalized their divorce in 2008, called it quits in 2006 after seven years of marriage. Witherspoon married Jim Toth in 2011 and welcomed son Tennessee in 2012, while Ryan shares 10-year-old daughter Kai with ex Alexis Knapp.
After Witherspoon reposted Deacon’s photos, Kate Hudson — who is the mother of Ryder, 18, Bing, 10, and Rani, 3 — was in disbelief of how grown up Deacon was.
“What happened to our children?!?!?!” the Almost Famous actress commented.
Leah Remini, for her part, got emotional as 17-year-old Sofia attended her final high school dance.
“Last night was Sofia’s senior prom. Senior year is filled with exciting milestones but it doesn’t make it any less sad for parents when we wonder how time flew by so fast,” the King of Queens alum wrote on May 22 via Instagram.
The actress shares the teenager, who rocked an emerald green dress, with husband Angelo Pagan.
Remini added: “Angelo and I couldn’t be prouder of the young woman Sofia is becoming. But I need this process to slow down.”
Angelo shared a video from the pre-prom celebrations, which included red, black and white balloons and balloon letters that read, “Prom 2022.”
“I can’t even say how I’m feeling because I’m really so overwhelmed with emotion,” he said. “My little girl is graduating and off to college. Crazy.”
Scroll through to see photos of celebrity children at prom: