Vlaar was El Ahmadiâ€™s captain last season as the duo helped Feyenoord finish runners-up in the Dutch top flight and book a Champions League spot.
â€śI was looking forward to linking up with Karim again,â€ť said Vlaar.
â€śWe sat next to each other in the dressing room at Feyenoord. We know each other really well.
â€śTo have Karim here makes it easier for me to settle and become a member of the group. I will feel at home.
â€śIt certainly makes it easier. But even if that wasnâ€™t the case you find your way. We will see what happens.
â€śI have heard some good stories from Karim about the club, the way of living here in Birmingham â€“ the area is fantastic â€“ and the training.â€ť