Leonardo Bonucci has rejoined Serie A champions Juventus from AC Milan, while striker Gonzalo Higuain has moved the opposite way on a season-long loan.
Milan will pay €18million (£16.3m) for the loan of Higuain, with an option to then secure his signature on a permanent deal for €36m (£32.6m) thereafter.
The Argentina international joined Juve from Napoli for a then domestic transfer record fee of £75.3m in 2016 and scored 40 league goals in two seasons with the club.
Defender Mattia Caldara also left Juve to join AC Milan as a part of the swap deal involving Bonucci between the two rival clubs.
Both transfers (Caldara and Bonucci) are worth 35m euros (£31.2m) each.