Boateng, 31, has joined Italian side Sassuolo after only a single season with Die Adler, where he won the DFB Cup in the final against Bayern Munich.
It marks his third different league in three successive seasons after his 2016/17 spell with Las Palmas in LaLiga.
However, his return to Italy is said to be motivated by his desire to be closer to his family as his partner Melissa Satta resides in her home country.
"I agreed with Prince when we signed him that we would never stand in his way if he wanted to leave," the club's sporting director Fredi Bobic told the club's website.
"He expressed that wish now because he would like to be playing where he sees himself settling to live, which is why I have obviously kept my word.
"We have a lot to thank Prince for. He was an outstanding leader, both in human terms and sportingly, and we wish him and his family all the best for the future. Kevin-Prince Boateng leaves Eintracht and the Bundesliga as a winner."
While Boateng paid homage to the German top-flight side; "With victory in the Cup, my career in Germany has gone full circle and I am leaving Eintracht with a positive feeling.
"It was an excellent year for me and I will never forget my time in Frankfurt.