The Alright hip-hop star visited Washington, D.C. in October (15) for a performance, and he stopped by the Oval Office for a chat with Obama about the social causes he writes about in his music, including racism, crime and gang life.

Photographs of their meeting have now been used in a video to promote the Pay It Forward scheme, which encourages adults to mentor inner city youngsters.

Narrating the video, Lamar says, "As a kid, having a mentor was vital to me or always been there when it counted, allowing me to make some of the important decisions while growing up. So it's only right that I mentor a younger person with the same wisdom that was given to me. If it helps the next kid become a better person in life, I will forever be aware of my influence and pay it forward.

"I look at where I'm at today and realise that most of my success is owed to the mentors that was (sic) in my life. I sat down with President Barack Obama and shared the same views. Topics concerning the inner cities, the problems, the solutions, and furthermore embracing the youth, both being aware that mentoring saves lives."

Obama's senior adviser Valerie Jarrett told the rapper was nervous before the meeting, saying, "(He) was a little nervous - bless his heart, he's really a very nice young man, and the president said, 'Can you believe that we're both sitting in this Oval Office?'"