Always be careful not to kick a wasp nest.

That’s a lesson Charlie Hunnam learned the hard way, he told Jimmy Fallon during an appearance on “The Tonight Show” on Monday.

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“A very strange thing happened to me when I went camping. I went out looking for firewood one day, and it was the end of the season and it was kind of picked dry, so I was pretty far from my camp,” he related.

“I saw three trees fallen into a triangle, and in between those trees were the motherload of firewood. So I said ‘Alright, here we go’, and I got up and I was crouched down picking up firewood, and all of a sudden, wham!” Hunnam recalled. “Like a snake bite in the perineum.”

But things turned out to be even worse than expected for the star of “The Gentlemen”.

“I looked down and there was no snake, so I was trying to process what could have happened, and bam!” he said. “Another shrill pain in my a** cheek, then one in the back of my head, and then one under my armpit. And I realized I was under siege from yellow jackets. I’d kicked over a nest of yellow jackets, and as I was processing this angry swarm coming at me, I got stung about another 10 times.”

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That’s when Hunnam went on the run… naked.

“I ripped all of my clothes off. I kicked my shoes off, and I took all my clothes off, and then put my shoes back on and continued sprinting completely naked. And this is all true,” he told Fallon.

“I realized at that moment that I was actually inside a nightmare. A recurring nightmare. I, for many years, had this recurring nightmare that I was sprinting for my life naked in a forest,” he said. “And in that moment I was literally living my recurring nightmare. And I haven’t had that dream since, so it was something of a prophecy.”