Rebic, 26, proved to be an inspired loan recruit for Milan last season, scoring 12 goals in 30 appearances.
And the Rossoneri have made his stay permanent, signing the Croatia forward on a contract until 2025.
He has taken a new shirt at Milan and will wear the number 12 from now on.
🇭🇷 Rebić 12 🔴⚫
A new season, a new adventure, a new number
— AC Milan (@acmilan) September 12, 2020
Rebic was part of a loan swap last year that saw Portugal striker Andre Silva head the other way to Frankfurt.
Like Rebic, Silva had a successful loan spell, finding the net 12 times in 25 appearances.
Milan spent €38m to sign Silva from FC Porto in the summer of 2017, but he had a difficult first year at the San Siro.
Neither Milan or Eintracht have disclosed the transfer fees for Silva and Rebic.
New chapter, the same ambitions! 2️⃣0️⃣2️⃣3️⃣ pic.twitter.com/tfmrBT69AM
— André Silva (@andrevsilva19) September 10, 2020