Former Town assistant manager Willie Donachie has joined Millwall in a similar role. Donachie left the Blues after Jim Magilton took over as manager last month.
New Millwall manager Nigel Spackman announced the new appointment: "Willie is a fantastic coach, very organised and enthusiastic and the players will enjoy working with him.
"The appointment of my assistant has to be the right choice. We will do a lot of work together and consequently I need to trust him. I trust Willie completely and his experience will be invaluable for us.
"He has worked in the Premiership, coached Manchester City and Oldham to promotion, his track record speaks for itself."
Donachie said: "I enjoyed working with Nigel previously at Sheffield United and I'm really looking forward to doing so again.
"He wasn't the only reason behind my decision to come here though; I met members of the board and I was just so impressed with their enthusiasm and ideas.
"I can't wait to get started. I have already done a bit of homework, but I'm coming in very open-minded.
"Our aim here is to add to what Millwall have had in the past and make this a difficult place for other teams to come to.
"Our team will be hardworking, but with a bit of class, and one that hopefully our fans will enjoy watching."