Tom Cruise — desperate for a blockbuster hit — snapped while filming his latest movie, sources say.

The fading superstar’s bizarre behavior on the "Knight and Day" set rocked his marriage to Katie Holmes, and crew members feared he was cracking up, according to insiders.

"No one has ever seen Tom so close to the edge," an insider told The ENQUIRER.

The 47-year-old actor startled crew members with his weird tics, and insisted on changing the movie’s score just weeks before its June 25 release, said the insider.

"Tom developed this bizarre habit of referring to himself in the third person," the source said. "He’d say things like, ‘Tom Cruise is an action star — he’d never have salsa music in a film!’"

And with her husband manic on the set, Katie crumbled, said the source.

"At one point, she cried, ‘Tom’s so stressed out that I don’t know him anymore. I just don’t know how much more I can take,’" said the insider.

Get all the details in this week’s ENQUIRER — on newsstands now!