A lucky pet owner bought a cat off Craigslist and accidentally ended up with one of the rarest felines in the domesticated cat world.

In a post shared on Instagram on Monday, under the username @xxycalico, the poster explains that after seeing a calico cat listed on Craigslist, she fell in love and decided that she was the one.

"Went to pick her up as soon as possible. Immediately serving sass and violence. I named her Josie," the poster said.

However, she soon started noticing something strange about her new kitten, though she would never have expected what the veterinarian was about to tell her.

"It only took a couple days for me to start questioning if this was a female cat. So I brought it up at her first vet appointment. The vet said there's no way it was a male cat, because calico cats have to have two X chromosomes," the pet owner said.

"But upon further inspection they confirmed that the cat was a male, which means he must have XXY chromosomes."

The veterinarian had the idea of changing his name to Joey, but according to the poster, Josie had already stuck, so she kept it.

"He grew up into the sweetest boy. He's slightly deranged, but he's the best boy around! Wouldn't change a thing," she said.

The poster told Newsweek that Josie turns 3 in October and he has a companion at home, his little cat sister Rue.

Dr. Ashly Smith, from Small Door Veterinary, told Newsweek that male calico cats are extremely rare, with estimates suggesting that only about 1 in 3,000 calico cats are male.

"Male calico cats are rare because the calico coloring is linked to the X chromosome. Female cats have two X chromosomes (XX), which allows for the combination of orange and black fur along with white," Smith said.

"Males typically have one X and one Y chromosome (XY), so they usually display only one color. However, in rare cases, a male cat may have an extra X chromosome (XXY), leading to the calico pattern. This genetic anomaly, known as Klinefelter syndrome, makes male calico cats both rare and usually sterile."

The video quickly went viral on social media, getting viewers from across Instagram. It has so far received over 12.3 million views and 645,000 likes on the platform.

One user, Bailey_mari3, commented: "The orange in him is STRONG."

Epwr_11 said: "Y'all forgetting the best part: he had tumbs!"

Bellasweetish added: "In Japan it is said that a male calico is a bringer of luck. Because they are so rare. That's why many maneki neko (lucky cat) are male calicos."

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