Chelsea boss Carlo Ancelotti admits he gaffed selling Gianfranco Zola while in charge of Parma.
Now 13 years later, Ancelotti faces Zola and West Ham United today.
"Probably I made a mistake with him because I wanted to play 4-4-2 and I put the players in the right positions but he wanted to stay in the centre like a striker," Ancelotti said.
"In that period, when there was this discussion, Chelsea offered him a good contract and he decided to go.
"I think it was a mistake. It was my first experience in Serie A and I was not able to change the system.
"I preferred to maintain the system that I knew well. For this, Gianfranco had a different decision to make. But a lot of time has passed since and now we have a good relationship.
"He would probably not have gone to Chelsea if I had changed the system, but he had a wonderful experience here at Chelsea and all the fans here remember his performances."