Not Nicholas Barclay

The Barclays family was happy and almost started living a normal life, but everything changed after the fingerprints and DNA results came out. Everyone was shocked, the results showed that this person was NOT Nicholas Barclay. This not Nicholas individual who has been living with them as their son for almost six months was an imposter. And the scientific results were right there to prove it. But the question was if he is not Nicholas Barclay then who is this guy?