Keaton, 75, posted an Instagram video entitled “male beauty” featuring 18-year-old Phillippe as the first image, with the actress narrating the compilation with compliments.
“Talk about beauty, Leonardo DiCaprio,” Keaton said. “Give me a break. I knew him when he was a kid.”
The Annie Hall star had accidentally used a black-and-white photo of the teenager, which Witherspoon was quick to correct in the comments section.
“Diane, the first one is my son!” Witherspoon wrote, with thousands of fans liking and replying to her comment.
Keaton then replied to her note with a series of embarrassed-face emojis.
The professional portrait of Phillippe bears a close resemblance to DiCaprio, 47, and fans agreed in the comments, while some said he looked like a young Heath Ledger.
“I was 100% convinced it was Heath,” one person wrote.
Among the other photos in Keaton’s male appreciation video were actors John Cassavetes, Robert Pattinson and Clint Eastwood.
Despite Witherspoon pointing out Keaton’s blunder, the clip remains on her Instagram.
Deacon is Witherspoon’s eldest son, who she shares with first husband Ryan Phillippe.
The pair also share Witherspoon’s lookalike daughter, 22-year-old Ava.
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