Woody Harrelson and Matthew McConaughey aren't just True Detective co-stars — they're also lifelong friends.

And in an incredible twist of fate, the famous besties also learnt they might actually be brothers.

The pair do share a remarkable resemblance, from their eye colour to their perfectly high cheekbones and pronounced chins. (Now you've seen it, you really can’t unsee it though, can you?)

The belief, they said, stems from an admission McConaughey's mum made while their famous families were holidaying together in Europe.

"You know, where I start and where he ends, and where he starts and I end, has always been like a murky line," Oscar-winner McConaughey said.

"And that's part of our bromance, right? My kids call him Uncle Woody. His kids call me Uncle Matthew. And you see pictures of us, and my family thinks a lot of pictures of him are me. His family thinks a lot of pictures of me are him."

Watch: Matthew McConaughey Best Actor Speech. Article continues after video.

"In Greece a few years ago, we’re sitting around talking about how close we are and our families," he continued. "And my mum is there, and she says, 'Woody, I knew your dad.' Everyone was aware of the ellipses that my mum left after 'knew.' It was a loaded K-N-E-W."

The actors knew what "K-N-E-W" meant. But could McConaughey really be a product of his mother Kay’s romance with Harrelson’s father, Charles? (Who, ICYMI, was a murderer...)

They did the math and realised that following a break in her marriage to McConaughey's dad, "Big Jim," Ma Mac may have crossed paths with Harrelson's father, Charles, right around the time Matthew was conceived.

And because Hollywood simply cannot let an iconic real-life drama go to waste, this whole wild scenario has officially been turned into a TV series. Genius, really.

Apple TV's new comedy series, titled Brothers, which comes out on September 23, opens every episode with the cheeky line: "Based on a true rumour."

In the show, Harrelson's daughter is going through a breakup, so he decides to take the family to fictional McConaughey's Texas ranch. Meanwhile, fictional McConaughey is flirting with running for governor of Texas.

They essentially play heightened, hilarious parodies of themselves.

Harrelson plays a hippie-anarchist, while McConaughey plays a cowboy-philosopher rancher who gets roasted by his family over his Lincoln car commercials. The impressive cast features Holland Taylor as "Ma Mac," Natalie Martinez as McConaughey's wife Valentina and Brittany Ishibashi as Harrelson's wife Joy.

"We need to not be afraid of leaning into more fictitious exaggerations of ourselves, not be afraid of playing slight parodies of certain expectations of ourselves, and with our relationships with each other and our families," McConaughey told Vanity Fair.

"So when we took the bridle off of sticking to what's so great about the reality, I think that's when we started to lean into just a little bit higher comedy."

And as for whether we'll ever find out if this hilarious series is actually rooted in real-life genetics? Don't hold your breath. It turns out we may never get a definitive answer on whether the show is based on cold, hard reality. Mostly because the pair don't look like they'll be taking a DNA test anytime soon.

"The thing is, we want to go for a test, but for him, it’s a much more big deal," Harrelson said on The Late Show with Stephen Colbert.

"I mean he feels like he is losing a father. But I’m like, no, you’re gaining a different father and a brother."

McConaughey also explained why he was hesitant to do a DNA test during his appearance on Ripa’s podcast.

"Look, it’s a little easier for Woody to say, 'Come on, let’s do [DNA tests],' because what’s the skin in it for him?" he said.

"It’s a little harder for me because he’s asking me to take a chance to go, 'Wait a minute, you’re trying to tell me my dad may not be my dad after 53 years of believing that?' I got a little more skin in the game."

Woody Harrelson's father, Charles Voyde Harrelson, was a contract killer who was arrested following a stand-off with police after shooting dead US District Judge John H. Wood Jr in May, 1979.

Woody was 11 at the time, and heard the news over the car radio after school pickup. At this point, his father was no longer in his life, having left Harrelson and his mum, Diane, years earlier.

The actor would later learn it wasn’t his only killing.

In 1968, Woody's father was paid $2000 for the murder of Sam Degalia Jr, a grain dealer and father-of-four in McAllen, Texas. In 1973, after an initial mistrial, Charles was sentenced to 15 years in prison, though he was released after five years for good behaviour.

In 1981, Charles was handed down two life sentences for the assassination of the judge. His son had already launched his acting career by this time (he was 20) and spent millions of dollars on lawyer fees to help his father — not because he thought he was innocent, but because he wanted to help his dad, with whom he also shares a birthday.

In a 2012 interview, actor Harrelson opened up about an eerie belief in Japanese culture about males who share birthdays with their father.

"They have a thing in Japan where they say if you’re born on your father’s birthday, you’re not like your father, you are your father," he told The Guardian.

"And it’s so weird when I would sit and talk with him, it was just mind-blowing to see all the things he did just like me. Idiosyncratic things. The way he laughed. The face, very similar."

This article was published in 2023 and has been updated with new information.

Feature Image: Instagram/officiallymcconaughey.