The former Albion left-back has spoken to media in Italy for the first time after his recent move to Milan.
Estupinan played for three different head coaches in less than three years with the Seagulls after his move from Villarreal.
But, given the press conference was in Italy, conversation inevitably focused on one of the three in particular.
Estupinan made his debut under Graham Potter and worked with Fabian Hurzeler last season.
But he arguably enjoyed his best times under De Zerbi, with whom he helped the Seagulls finish in a best-ever sixth place and move into Europe.
The Ecuador international also revealed he improved his language skills with the Italian boss.
Estupinan said: “I'll work hard because I want to repay the faith shown in me.
“I can't wait to win a lot of trophies with AC Milan, and I want to contribute to that.
“De Zerbi helped me to understand Italian, but I can't speak it yet.
“I'm happy to have been coached by him. He's a great coach, and he helped me a lot.
“I have fond memories of our two seasons together, and I'll try to utilise all that he taught me.
“The Premier League is so intense, very different from LaLiga.
“You have to run a lot, and the ball moves so quickly.
“De Zerbi taught me to improve my passing. I worked a lot with him and got much better at it. I'll try to keep developing at AC Milan."