Two weeks ago, I told you that Kenny Chesney was going to perform one concert this year.  (He's taking this year off...)  Well, he played the charity concert and even did a Johnny Cash duet with Reese Witherspoon!

The two stars sang 'Jackson' by Johnny Cash.  Witherspoon is familiar with the tune after her Oscar-award-winning performance as June Carter Cash in the film 'Walk the Line.'

The concert was to raise money for Drew Brees and Matthew McConaughey's charities, the Dream Foundation and the Just Keep Livin' Foundation.

Witherspoon posted a photo on her Instagram account of the two singing together!