Matthew Mcconaughey says 'White Boy Rick' is like his ''sad country song''.

The 49-year-old Hollywood actor stars in the Yann Demange directed flick as Rick Wershe Sr, whose teenage son Richard Wershe Jr. became the youngest ever FBI informant at the age of 14 and then went on to become a major cocaine dealer Detroit in the 1980s in the biographical drama.

McConaughey admitted it was a completely new ''challenge'' to take on the part of blue collar worker Rick and he tried to lace his performance with the type of melancholy which exists on some country music records, as he could relate to the father's sadness over the fate of his son.

Speaking exclusively to BANG Showbiz at the 'White Boy Rick' premiere in London on Tuesday night (28.11.18), McConaughey said: ''It's my sad country song. I've never had a role that's my sad country song. This is my sad country song and I've never played a role like that. I endeavour to take on roles that are different, that challenge me in different ways and scare me in different ways. I wanted to do my best to inhabit this man, also that fact that it was a great drama that told a great story, and even if it wasn't true it was one that I felt deserved to be told and put on the screen.''

Father-of-three McConaughey is very pleased he got to tell the story of Rick Sr - who passed away in 2014 - on the big screen and he did extensive research to ensure that her portrayed his real-life alter ego correctly.

He added: ''Yeah it wasn't fun research, it was a bad dad, and it's a sad dad. He's a bit of a loser and he's one of those guys that's full of the dreams but has no follow through, a lot of the one twos, but none of the can dos - single parent families born into poverty that are unable to break that chain and get out of it. I mean for me, I looked at people who were going through things. I started with fathers that I knew that wanted to raise their sons and be best friends with them. None of their son's turned out too well because they wanted to be best friends and they had no consequences, and the fathers couldn't give them consequences because they wanted to be best friends.''