"Although I came on in seven other league games and started against Bristol City in the FA Cup last month, I didn't feel established at Boro," he told Scotland on Sunday. "I was still the new kid on the block. My contract was up at the end of this season and my dad and I would have liked to have heard something from Middlesbrough but we didn't.
"Instead there were a few clubs from lower divisions who were interested and then Celtic came in and offered to sign me on a pre-contract. I'd been looking to secure my future but this was a dream come true, real fairytale stuff.
"My first reaction was: 'Let's get this done.' When a club the size of Celtic offers you the chance to join them then you don't think twice about it."