“After five years I could not hope to end this great experience in a better way,” the Ivorian wrote.
“A unique emotion – we are Italian champions! I am proud to have worn this glorious shirt and to have shared this journey with some fantastic companions.
“Thanks for everything. Thank you all. Your President.”
Kessie, 25, was born in Ouragahio in the Ivory Coast and began his career with Stella Club before securing a move to Atalanta in 2014. He made his senior debut with the Bergamo outfit but didn’t hit his prime until he went through loan spells with Cesena and then Milan. He joined Milan in a permanent deal in 2019.
He has since made 223 appearances for Milan, contributing 37 goals and 16 assists for the Italian giants. He served as a key part of the team that won the Scudetto this season.
Kessie has also earned 52 caps for the Ivory Coast national team.
Barcelona have already signed Kessie on a free transfer this summer and the deal will be made official imminently. He will add something different and unique to the Barcelona midfield.