SETTING up his camera, one little boy thought he'd come up with a foolproof way of proving Santa's existence for anyone who had any doubts.

But the youngster definitely wasn't expecting to capture his dog leaving a little surprise under the family's Christmas tree.

Footage posted on Twitter by his sister, who goes by @Intolisa, shows the boy positioning his iPad under the Christmas tree.

He can be heard excitedly telling the camera: "Hey, what's up guys. Well, I'm going to be catching Santa on video today because it is Christmas Eve, and yeah."

It then cuts to a clip, which appears to be much later on, showing a Chihuahua running and sniffing around under the Christmas tree.

The little dog then picks a spot - perfectly in frame - to leave a very different sort of gift to the kind the boy was intending to receive on Christmas morning.

His sister then shared his hilarious reaction as he reaches for his iPad and spots the small mess in the way.

Pointing at the pile of poop, he says to the camera: "What's up guys. That - you're probably wondering what that is - I think you guys know.

"Well, I'm going to pause the video and see what actually happened."

And social media users have been tickled by the clip - and it's been liked more than 450,000 times since being uploaded on Christmas Day.

One Twitter user replied: "omg, he's leaving a yule log for everyone under the christmas tree."

Another wrote: "I've already watched this four times. Think it knocks It's A Wonderful Life out of my top three Christmas movies."

While one social media user said: "Never has 'merry Christmas ya filthy animal' been more appropriate."

It comes as a mum reveals she gave birth under the tree on Christmas Day while her other kids opened their presents.

Meanwhile, ungrateful Brits put their unwanted gifts for sale on eBay just hours into Christmas Day.