The two Italian giants have spent the best part of this week discussing a sensational triple transfer, which sees two Juve players heading off to San Siro.
And the deal has now been finalised, with Higuain gearing up to star at his third Serie A club on an initial loan move, including a fee estimated at €18 million (£16m/$21m).
"AC Milan can confirm they have acquired the rights of Juventus footballers Gonzalo Higuain and Mattia Caldara," the Rossoneri stated on their official website.
"Gonzalo and Mattia are two important additions in the club's new era. Gonzalo Higuain comes to Milan in a loan deal until June 30, 2019 with a purchase option."
Caldara, meanwhile, spent just one month at Juventus following his move from Atalanta, but the defender leaves now as a makeweight in the deal to bring back Old Lady favourite Bonucci.
The two centre-backs, Milan confirmed, switch teams in a straight swap, with no further money changing hands between the clubs.
"Mattia Caldara comes direct, as part of the exchange that includes Leonardo Bonucci, who returns to Juventus," Milan added.
"The 24-year-old defender has signed a contract with AC Milan until June 30, 2023."
Both Higuain and Caldara underwent medicals in Milan on Thursday prior to the announcement, with the club publicising the pair's arrival in the city.
And the Rossoneri's announcement was swiftly followed by confirmation from Juventus that prodigal son Bonucci had come back just one year after leaving the club for San Siro.
"Juventus Football Club announces the return of Leonardo Bonucci after the defender completed his move from AC Milan," the club stated on its official website, confirming a five-year deal for the 31-year-old Italy international.
"After spending seven wonderful years in black and white, Leonardo Bonucci has returned to the club following a season at AC Milan.
"Bonucci began his Bianconeri career in 2010, emerging as one of the most promising young defenders in Italy, and he would go on to establish himself as one of the very best in the world in his role.
"Now, both Juventus and Bonucci are ready to start winning things again together.
"Welcome home, Leo!"