The Chiefs star made the revelation while chatting with reporters at Super Bowl Opening Night at Allegiant Stadium in Las Vegas on Monday ... sharing with the world that he's grown so close to his pop star girlfriend, she's actually allowed him to listen to some of her top-secret, unreleased tunes.

And, Kelce said he's been loving what he's been hearing up to this point.

"I can't wait for her to shake up the world when it finally drops," he said.

Swift revealed at the Grammys on Sunday night that her new project, "The Tortured Poets Department," will be dropping on April 19. On Monday afternoon -- just before Kelce took the podium in Sin City -- she unveiled the titles of the songs ... sending the internet into a frenzy.

Kelce didn't want to say much more about his GF's new work -- adding only "I can't give you anything; I leave that up to her" -- but he did heap a ton of praise on her throughout his Monday evening Q&A regardless.

The Kansas City tight end said he was proud of her for winning her 13th and 14th Grammys ... saying, "She's rewriting the history books herself." He then said he was hoping to add another Lombardi Trophy to match her new honors.

"I told her I'll have to hold up my end of the bargain and come home with some hardware too," he said.

Kelce did not confirm whether or not Swift would be in attendance Sunday ... though he called her the Chiefs' "No. 1 fan" -- implying that she'd somehow make the lengthy trek from Tokyo to watch him in action.