Seriously.

The former Yankees captain made the surprising -- and hilarious -- revelation while playing a game called "True Confessions" with Jimmy Fallon and Rita Ora on Wednesday night's "The Tonight Show."

Jeter was forced to pick one of two topics, and his two cohosts had to guess if he was telling the truth or not.

"I once wore a thong, in public, in front of thousands of people," Jeter said.

Both Fallon and Ora thought it was a fib -- but the ex-NY shortstop said it was, in fact, a real tale.

Jeter explained ... back in 2002, he got a new teammate who swore up and down that wearing a golden thong would get him out of any slump.

Jeter initially thought it was a load of B.S. -- but at the start of the '04 season, he hit an offensive rut that he had never seen before.

"Every day I'd walk in, [my teammate] would point at the thong," Jeter said. "So, finally, I wore the thong."

First pitch of his first at-bat? Home run for Jeets.

"Yes, yes," Jeter said. "That is true."

The game was said to be the Yanks' April 29, 2004 contest against the Oakland A's. Records show he was in an 0-for-32 skid before cracking a dinger off Barry Zito at Yankee Stadium.

As for who the golden thong's true owner was? According to a 2015 interview on the Dan Le Batard Show, it was none other than Jason Giambi.

"The golden thong is legendary," JG said during the '15 discussion on ESPN Radio. "It's never not gotten a hit."

By the way, if you're wondering about the hygiene of it all -- don't worry, Jeter said there was no thong-to-skin contact.

"I had shorts on underneath," he said. "I put the thong over the shorts."