When retired US legislator Steve Lindberg stepped out of his front door with his camera on Monday, he was hoping to snap some wildlife for his Facebook page.
Since 2012, he has uploaded a photo every day of wildlife in his native Michigan.
He wasn't too optimistic due to the winter weather driving many species towards warmer temperatures, so he was pleased when he spotted a river otter eating a fish on the ice.
"I thought: 'Oh jeez, I got my photo for the day,'" Mr Lindberg, 75, told the BBC.
But as he strolled back to the car with his dog, he noticed a strange looking deer.
"I have thousands of photos of white-tailed deer but I immediately recognised that this one was unusual... he had this little mess of antlers on top of his head," he said.
He took a few shots and drove home, thinking little of it.
But when he uploaded the photos to his computer, he noticed something.
"I went: 'Wait a minute, this deer has three antlers!' I'd never seen one before."
Mr Lindberg was expecting to hit around "100 likes and a few comments" on Facebook but the post started to take off with intrigued members of the public analysing the rare photos.
Large-animal veterinarian Steve Edwards told the Detroit Free Press that the deer was a "one-in-a-million" find.
As is often the case on social media, not all of the attention has been positive, with some accusing Mr Lindberg of editing the image. He uploaded other photos to quash those allegations.
"I've stopped reading what people are writing because I've been accused of photoshopping... I've been told: 'I want to know where it is because I want to kill it,'" he said.
Mr Lindberg, who used to hunt but stopped years ago, has decided to keep the exact location of the deer a secret to protect it.
When he returned later in the day, the deer was in the same spot. But the next day, he was nowhere to be seen.
"He's gone on to greener pastures, so to speak," he said.