Michael Madsen was unaware of Justin Bieber`s popularity

Los Angeles: Actor Michael Madsen`s children were shocked when they got to know their father had no clue about teen sensation singer Justin Bieber.

The 55-year-old starred in Bieber`s song "As Long You Love Me" as the father of singer`s girlfriend decided to do the song because he was popular among the teenagers.

"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`," a website has quoted him as saying.