The 'Hansel and Gretel: Witch Hunters' actress admits she has had a crush on the actor since she was a little girl and saw him 'Titanic', but is embarrassed to meet him as she probably wouldn't be able to control herself.
She explained: ''I was never a groupie but I did have my crush - Leonardo DiCaprio. I was 12 or 13 and I had a poster of him on my wall. 'Titanic' was out then and it was huge. It seems so funny to me now!''
The 27-year-old beauty added that she was worried about the 'Django Unchained' star finding out about her crush if they were to ever meet.
She said: ''He probably doesn't know who I am. It would be awful if he found out and I met him!
''I'd probably drool.''
Gemma then quipped: ''I wish I hadn't told you that now. I'm going to get found out - just say that I admire him!''
However, the British actress claimed she only found his acting talents attractive.
She added to Britain's OK! magazine: ''He's an amazing actor. Because I was always into acting, my crush was always on actors.''