Billy Clarke was an unused sub for Colchester as the U's confirmed their promotion to the Championship with a 0-0 draw at Yeovil. Phil Parkinson's men finished second in the table behind Southend.
Ex-Town central defender and Colchester captain Wayne Brown missed the game with a last minute hamstring injury.
The U's elevation to the Championship means next season will see the Blues will face their nearest league neighbours in competitive action for the first time since 1956/57.
Other former Town employees with Colchester are ex-midfielder Geraint Williams, who is assistant manager at Layer Road and coach/scout Brian Owen, who was on the Portman Road staff during Bobby Robson's time as manager. U's goalkeeper Aidan Davison had a spell on loan with the Blues in 1996.
Clarke's spell with Colchester consisted of two starts and four substitute appearances.