`Harry Potter` star Rupert Grint says joining the cast of the wizard saga at the age of 11 meant he lost "a few friends".

Grint says that he has always struggled to "figure out" whether people in his life were genuine or if "they had ulterior motives".

"You'd always worry about whether it was a genuine thing - and I think that goes with any kind of relationship, even friendships,` mirror.co.uk quoted him as saying.

"It took me a while to figure out whether someone was genuine or they had ulterior motives...I left school at quite a pivotal time...when you're just making friends and stuff.

"So whenever I came back, bonds I had made before had all got a little bit weird. I did lose a few friends but on the whole it's all been pretty good,` he added.