Los Angeles, California - He was the only one not allowed to go to the Christmas party with the other dogs – and he had to watch them romp around from his cage! Why was this little four-legged friend ignored like this?

An Instagram video tells the "saddest Christmas story," according to creator Carol.

The clip begins with numerous dogs with their owners at the festive gathering.

But a subtitle warns, "Wait until the end..." before the camera pans through the hall in Los Angeles and stops at a room filled with dog cages.

All of the kennels there appear to be empty – except for one, in which sits a small four-legged friend with a festive blue bow around his neck, looking the saddest dog you can imagine!

It's not just the camerawoman who is touched by this sight, but also many Instagram users. Since last week, the video has received tens of thousands of clicks – as well as many a sad comment.

In an interview with Newsweek, Carol revealed the real story behind the heartbreaking video.

"The party was a friend's holiday gathering here in LA," the woman explained.

"We spotted the dog in the cage looking on at the grooming area. We don't know who the dog was, but it looked like they just wanted to join the fun."

Carol later found out that the dog had an appointment at the groomer, so at that moment, the four-legged friend was just waiting to be picked up by his owner.

"Without the owner's permission, we could not have him over for safety reasons," Carol explained, so unfortunately, the woman and her friends' hands were tied.

"The moment was so relatable – every pup wants to be included in the celebration," Carol added.

Thankfully, there's one upside to the situation: the video has become a viral hit!

"The reaction has been wild. We're happy it resonated with so many people," Carol said.