He had been on loan at the Serie A club.
Cork City have confirmed that centre-back Cathal Heffernan is making a permanent switch to Serie A champions - AC Milan.
The 17-year-old made 16 appearances with the club's under-18 side after joining on loan in January.
Heffernan made his first team debut in the final game of the 2021season for Cork City where he joined from Ringmahon Rangers in 2019.
The League of Ireland club haven't revealed any contract or financial details in relation to the transfer.
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