Michael Madsen was baffled when he was asked to appear in a Justin Bieber music video earlier this year (12) because he had never heard of the teen sensation.

The Kill Bill star acts out a fight with the Baby hitmaker in the gritty promo for As Long As You Love Me, in which the actor plays the overprotective father of the singer's girlfriend.

Madsen admits he was initially reticent about accepting the video offer, and it was only when his sons told their father of Bieber's worldwide fame that he agreed to the cameo.

He tells ETOnline.com, "It wasn't something that I originally would say yes to, but I went to my kids and I asked them, I said, 'Who is Justin Bieber?'... and my seventeen-year-old son, he put his hand on my shoulder and he goes, 'Dad, don't you know who Justin Bieber is?' I said, 'No, I really don't'."

Madsen was also impressed with the script he was sent for the promo: "It was like a 15 page synopsis, it was almost like story-boarded, almost like a mini movie."