Charlie Hunnam was camping in the woods last year when he went out to collect wood for the fire, only to stumble upon a wasp nest, with the insects inside turning angry when he accidentally kicked over their home.
The 39-year-old actor had to sprint naked through a forest to escape the attack.
He recalled: "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.
"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! Like a snake bite in the perineum."
After explaining that the perineum is the "sweet piece of no man's land between the anus and the scrotum", the star went on to reveal that the sensation wasn't caused by a snake, but instead a swarm of "yellow jackets", which is another name for wasps.
He continued: "I looked down and there was no snake, so I was trying to process what could have happened, and bam! Another shrill pain in my a** cheek, then one in the back of my head, and then one under my armpit. And I realised 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."
Charlie ran from the wasps, but when he stopped for breath he was stung again as the wasps had chased him down.
He then decided to shed his clothes and continue running, in an attempt to get the insects to leave him alone.
Speaking during an appearance on The Tonight Show starring Jimmy Fallon, he said: "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.
"I realised 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. 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."