Paramedics loaded Thomas Markle into the ambulance in Tijuana, strapped an oxygen mask to his face and transported him around 9:30 PM to a hospital across the border in Chula Vista, CA.

Markle was admitted after fearing he was suffering a stroke. Thomas couldn't actually speak to paramedics, and had to write down his symptoms on a piece of paper.

You'll recall, Meghan's dad said he suffered 2 heart attacks right before her 2018 wedding to Prince Harry.

That happened just as he was in a tense standoff with his daughter and the Royals because he'd staged pics of himself getting ready for the wedding -- and some people accused him of faking the medical crisis for sympathy. He never ended up going to the wedding, after all.

It's unclear what Thomas' condition is right now, but one of his close friends says he remains hospitalized.

Markle had recently said he would be attending Queen Elizabeth's Jubilee celebrations in June. Looks like he might have to cancel yet another UK trip.