So, in this thread, lets try listing all the footballer who returned to their former club or were reunited with former manager.

Return:
Hummels to Bayern
Gotze to Dortmund
Pogba to Manchester United
David Luiz to Chelsea
Cuadrado to Juventus
Alvaro Morata to Real Madrid
Oliver Torres to FC Porto
Christoph Kramer to Borussia Mönchengladbach
Florian Thauvin to Marseille

Reunion:
Schurle with Tuchel
Zlatan with Mourinho
Wanyama with Pochettino
Krychowiak with Emery
Nolito with Pep

I'm sure I'm forgetting a tons of them, please add those you think of and I will update the list as much as I can. :D

Returning players:

Alvaro Morata to Real Madrid
Oliver Torres to FC Porto
Christoph Kramer to Borussia Mönchengladbach
Florian Thauvin to Marseille