Kanye West's friend John Legend: He started to degrade after his mother died

American singer John Legend has claimed that the death of Kanye West's mother in 2007 caused the controversial rapper's "downfall".

The "Ordinary People" singer detailed his relationship with West, which dates back to the beginning of his music career, in an interview with The Times.

The 46-year-old, whose real name is John Stephens, signed a record deal with Kanye West's GOOD Music label in 2004 and fondly recalled that period in the star's life.

"He had so much optimism, so much creativity," Legend said. "It's sad, sometimes shocking, to see where he is now."

Commenting on West's views on Judaism and Adolf Hitler, Legend said: "I didn't see any signs of what we're seeing now, his obsessions with anti-Semitism, anti-blackness, and it's sad to see his degradation."

When asked what might have caused this decline, Legend replied: "I don't think we're qualified to psychoanalyze him, but after his mother died in 2007, there was definitely a change. His decline started then and it seems to have accelerated recently."