The 24-year-old joins the Rossoneri for a reported €28m (£24m) and becomes their seventh signing of the summer after Ruben Loftus-Cheek, Christian Pulisic, Noah Okafor, Luka Romero, Tijjani Reijnders and Marco Sportiello.
Chukwueze will wear the number 21 shirt at AC Milan and departs Villarreal following a productive six-year stay, having joined the Yellow Submarine's youth setup from Diamond Academy in 2017.
The Nigeria international came up with 37 goals and 31 assists from 207 appearances in a Villarreal jersey, and he was a part of their 2020-21 Europa League-winning squad under Unai Emery.
Chukwueze also helped Villarreal reach the semi-finals of the 2021-22 Champions League, before enjoying another strong season in 2022-23 with 13 goals and 11 assists from 50 matches in all tournaments.
A 28-cap Nigeria international, Chukwueze has scored four goals for his nation and helped the Super Eagles finish third at the 2019 Africa Cup of Nations.
The attacker could make his Milan debut in a friendly against Monza on August 8, as he is not expected to link up with Stefano Pioli's squad for their final USA tour matches against Juventus and Barcelona.
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