Thommo had no hesitation when it came to turning his back on Newcastle's Gallowgate for the one in the East End of Glasgow.
He said: "Newcastle is a special place and a unique club but my memories of playing for Celtic made it a no-brainer when I was asked to come back and coach the club.
"I'd have been here at the end of last season if it was possible but I couldn't gamble my job at St James' Park on an eight-game trial period.
"We've got a nucleus of good players at the club and the manager will buy well. It was my ambition to return and I believe we can do well together.
"The job we have is to convince the Celtic fans to believe in us and fill the stadium once again."