A woman rushed her beloved pet to the vet after becoming concerned about her dog's lethargy, only to receive a hugely unexpected diagnosis.

TikTok user @a.niyah15 is the proud owner of 3-year-old American bulldog, Sky, and has shared multiple clips of the pet to her account over the years. But one video has gone viral after it ended with a surprising twist.

Posted on December 13, it begins with Sky sitting in a vet's office, along with the words: "POV [point of view]: You bring your dog to the vet because she seems very lethargic."

The clip then switches to show, as her owner described it: "Her 'water' breaks and we find out that our dog is pregnant and in active labor."

The video goes on to show a montage of Sky's owner comforting her after the birth of one single puppy, with one photo showing Sky looking utterly baffled, and the next showing the new mother smiling at the camera, as her puppy latches on to feed.

Her owner wrote that Sky "didn't know she was becoming a mother," but "at least she only had one pup." Newsweek has contacted @a.niyah15 on TikTok for comment on this story.

The montage continues, showing mother and puppy curled up together as the newborn grows bigger and stronger, learning to stand, walk and even giving his first few high-pitched barks.

The owner wrote in the caption: "The biggest surprise of the year. He is now 3 weeks old and we are trying to find unique/ cute puppy names."

That caption bodes well for commenters who pleaded with her to keep the mother and puppy together, such as one who wrote: "Only 1 pup? You gotta keep him!"

While it is unusual for a dog to have only one puppy, it can happen. Litter sizes can change depending on the mother dog's size, age, health and diet, while inbreeding can also lead to a smaller litter count.

Other commenters offered name ideas, with one suggesting "call him Uno," and another writing: "Juan because he's the Juan and only!"

Some asked how they could have not realized Sky was pregnant, as the owner said in the comments that they went to regular checkups but even the vet couldn't see anything. One shared: "This happened to me. My dog [had] four puppies on my pillow while I was sleeping."

Sky's owner later shared an update on the mother and puppy, thanking everyone who had helped the video explode in popularity, with over 1.9 million views since being posted.

She assured viewers that they did plan on keeping the puppy, and were taking all the name suggestions into account. In the end, they wrote three names on pieces of paper, and let the puppy choose himself; eventually, the tiny pup wandered over to the piece of paper with his new name: Capo.

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