BVB meet Rudiger and Real Madrid in the Champions League final on Saturday.
Fullkrug said: "He's a good boy, I love him. I like him because he's very honest, even if he's aggressive.
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"In training he's the same: he's a natural leader. He comes towards you and it seems like he wants to kill you (laughs). But I'm like that too and I love playing against this type of opponent.
"You can say that it is the strongest team in the world, with a gigantic history, but that is precisely what makes this final more captivating. Everyone wants to play these matches.
"It will be a beautiful, perfect final, in a historic stadium."