Ever wondered if there is someone out there who looks almost identical to you, but is in no way related to you?
No? Shannon Lonergan, 21, from Ireland, did. She discovered that she looks strikingly similar to Sara Nordstroem, 17, from Sweden.
Shannon said: "It's like a stranger but you know them. You can trust them because they look like you. There was no awkwardness ever."
Shannon and Sara were keen to learn a bit more about their similarities. With that in mind, they visited Professor Tim Spector at King's College London.
Using an advanced facial mapping system, the genetics expert studied their faces and found that - despite having no relation whatsoever - the pair shared a 90 percent facial similarity.
Shannon is not alone. Niamh Geaney, also from Ireland, set out to find her doppelgangers and successfully managed to find not one, not two, but three lookalikes. Two - Karen and Irene - in her native Ireland, and another - Louisa - in Italy.
Niamh told Sunday Night: "It's really cool but it's weird. You meet these people who look almost completely like you, but yet behind that you have different personality traits... even though you look the exact same.
"You think you're special and unique and there's no one in the world that's like you, and then you meet someone who looks identical to you and you realise you're not as unique as you thought you were."
In some of these cases, it's not just appearances that make doppelgangers similar. Neil Richardson and John Jemison aren't just lookalikes, they're behave-a-likes too.
When Neil moved to Braintree years ago, people kept saying hello to him in the street, convinced that he was John. Once, he even had to prove to a shop owner that he wasn't John.
Eventually, the pair met at a history tour and realised that they have similar interests including poetry, both met their wives and proposed within two weeks, trained at the same college and became religious studies teachers.
Think that's weird?
Both of their sons play the didgeridoo.
Now that is weird.
However, it turns out that there is at least some strange reasoning behind their similarities. They also did the test with Professor Spector and, as well as finding out that they also have a 90 percent facial similarity, they also share a common ancestor.
Somewhere down the line, at least, they are distantly related.
That still doesn't explain the didgeridoo thing, though.