"Beckham is a real gentleman and he is also a bit shy," former Arsenal midfielder Flamini told Sky Sport 24.
"He is a very hard worker and it's great for Milan to have someone like him in the squad.
"I'm really happy that he is coming and so are the other players here. I trained with him for three months and he is a great person on and off the pitch."
Milan's summer signing also gave his opinion on Inter boss Jose Mourinho, who continues to divide opinion in the peninsula.
"Everyone loves Mourinho in England because he won so much with Chelsea," Flamini said.
"I think Jose is someone you either love or hate but personally I think he is a great Coach."