What do you do when one of the most famous musicians of all time hauls himself up on stage beside you? You take a deep breath and keep singing.

That's what happened to musician Grayson Erhard at the weekend, when he was playing a music conference at a hotel in Anaheim, California.

Erhard was strumming his guitar to 'Superstition' when the one and only Stevie Wonder walked into the lobby of the Anaheim Marriott, heard him playing and decided to join him. "The guy was so excited when he saw Stevie and said he was sorry but he didn't know the words to the second verse," said Marcy Kraft, who captured the performance on video. "So Stevie offered to sing with him and he whispers the lyrics as they sing together."

The pair duetted on 'Superstition', with Wonder dedicating the song to the march in Washington and 'all the women of the world, because you are the reason we are here'.

Watch it below (click video to play):