Spike Lee arrived at Cannes this year to premiere Highest 2 Lowest alongside Denzel Washington, only to find himself serenading beachgoers with Rodgers & Hammerstein classics when questions turned to his next venture—a movie musical. The informal gathering at Carlton Beach, soundtracked by James Brown’s “The Boss,” took an unexpected turn when Lee, sunglasses on and feet in the sand, broke into “Oh, What a Beautiful Mornin’,” before deflecting talk of adapting the legendary songwriting duo’s work for the screen.

Lee’s reluctance surprised onlookers. Festival-goers had hoped for insight into his proposed musical project, first reported by Deadline in mid-May. Instead, he laughed off suggestions—“maybe we’ll tackle ‘The Surrey with the Fringe on Top’ next,” he quipped—then tuned out, returning to reciting favorite lines from Oklahoma! without committing to any details. Social media lit up with clips of Lee’s impromptu performance, reigniting speculation...