Speed, who represented Leeds, Everton, Newcastle, and Sheffield United and won 85 caps for his country during his playing career, tragically died at his home last year at the age of 42, leaving the game in a state of disbelief.
It came at a time when Welsh football was experiencing an upturn in fortunes with their former midfielder guiding the national side from the dugout, leading them to four wins in five games before his passing.
Ex-Fulham boss Coleman was handed the unenviable task of replacing his former international team-mate at the Millennium Stadium, and admits that he is still struggling to get over the loss of a close friend.
"Forget the football, Gary was a great guy, different class," said Coleman told ITV Sport. "I was lucky enough to have known him for a long time. He's greatly missed - I still miss him. I will always miss him.
"I can't believe it's a year ago. You don't ever forget something like that. I will probably never get over it. You try to deal with it as time goes on.
"But you don't forget someone like Gary. We never will.
"It will be a difficult day and Christmas will be difficult for his family, but we are all here to support them."
Since Coleman took up the reins from Speed in January, Wales have managed to win just once in seven games, and the he acknowledged that the players are still coming to terms with their bereavement.
He added: "I think people forget about the players. People just think they have to go out and get results. Of course, Gary's death was bound to have affected them.
"Players hold a lot of their emotions in. The dressing room is not the place where you show emotion.
"You hide everything. They will have dealt with it in their own time and space. It's been very hard for them and the players have handled it really well.
"You can't prepare for something like that because you don't think it will ever happen. When it happens it is a massive shock and surprise."