The Morocco striker signed permanently with Fener earlier this week.
Taking to social media, En-Nesyri stated: "One day, when I was little and lived in Fez, a person told me that the facts, the actions of every human being are worth more than a thousand words. All my life I have tried to realise this idea, always with love and absolute commitment to those who welcomed me with affection. This is why this letter is so difficult for me Fútbol Club.
"Today I say goodbye to my home, understanding the situation. During all these years it was clear to me that I didn't want to leave. Now I do it with the satisfaction of having defended your championship,
"I leave with titles, with goals, but above all with unconditional love. Forever. I want to take this opportunity to thank the president José María of Nido Carrasco, all the coaches I have had, my teammates and a fan I will never forget.
"Thanks, sivillistas. I will carry you forever in my heart. Now I arrive at a historic club like Fenerbahçe ready to give everything. They have shown me a very important trust and I want to help achieve all the objectives set. I am very excited and eager to respond to so much love.
"Goodbye, Sevilla Fútbol Club; Come on, Fenerbahçe."