Rihanna and the crowd at her "ANTI" tour were stunned and left wide-eyed by a fan at her concert who sang with a powerful and perfectly pitched voice.

Rihanna's expression said it all when she lent her mic to a fan, Terah Stewart, at her tour stop in Cincinnati, when singing the "Four Five Seconds" track, which also features Kayne West and Paul McCartney.

The audience also gave a loud shout when they heard the fan singing.

Rihanna sang, "Cause all of my kindness -- " and gave the mic to Stewart, who continued, "is taken for weakness."

Stewart said on Twitter that the moment of singing with Rihanna was overwhelming for him too. "Y'all don't understand how long I have been riding for @rihanna. I will never forget this. She followed me too," he tweeted.

Here is a peek into the awesome fan experience: