Travis Kelce was in the mood for his signature frozen custard, so he hit a drive-thru ... and he gave one lucky worker a fat tip for fulfilling his cravings.

We've got the sweet scoop ... Travis rolled up to an Andy's Frozen Custard in Kansas City, MO Thursday night and ordered the Travis Kelce 87 Concrete frozen custard ... and he stunned the girl who was working the drive-thru when he pulled up to the window.

The employee, who owns Hidden Files Studio clothing brand, tells TMZ ... the Kansas City Chiefs star was super "down to earth and humble" and let employees take pics with him. She says he thanked her manager and expressed gratitude for his fans.

With his $6 custard in hand, we're told Travis left a fat $90 tip to show his appreciation. We'll save ya the math ... that's a 1,500% tip!!!

For those wondering … bride-to-be Taylor Swift was NOT with Travis at the drive-thru. We’re told he was with a friend and they didn't say a peep about Taylor or their impending wedding.

As we first reported ... Travis and Taylor are tying the knot July 3 in the middle of Manhattan.

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No word if 87 Concretes are on the wedding menu.