Here's the deal, Timothee was at an art show last Friday in Santa Monica ... and appeared to be waiting out front for a ride, which is when Kylie's Lincoln Navigator pulled up with her security guards in the front seat.

We're told the actor quickly jumped in the back of her ride, while one of Kylie's guards drove Timothee's Escalade behind them. The cars ended up next door at L.A. staple Tito's Tacos, with Kylie's team getting food and bringing it to the back seat -- where Timothee and Kylie were sitting.

Security kept a tight detail outside the car for about 30 minutes before they drove away. Now, while Kylie's never seen ... who else would be in her car sneaking tacos with Timothee?

Also, he had his own car at the art show, so what's the need for a ride then? Hmm ... 🤔

As we reported, fans have been going nuts over the rumor that they're an item -- and, as we reported, one of her SUVs was at Timothee's home Thursday.

So far, neither is confirming the romance rumors.

One thing's for sure, things are starting to get spicy ... and we don't mean the tacos.