Dorrington has joined Aberdeen on a season-long loan, having helped the Dons win the Scottish Cup last season.
"I had six months here last season, and it was the best six months of my footballing life; winning the cup, playing lots of games, gaining new experiences," said Dorrington.
"As soon as I heard Aberdeen had come back in for me it was a no brainer, I just wanted to meet the team straight away."
He wanted to come back
Dons boss Jimmy Thelin added, "He played an important part in the squad in the second half of the season and with the campaign ahead we will need strength in depth to be competitive across all competitions.
"Alfie settled well and made a real contribution so it's always pleasing when a player shows a strong desire to be at the club.
"He recognised this is a good opportunity for him to be playing his football at a high level and in a good environment where he can continue to develop."