He will play the festival Saturday night at 10:30 p.m. EST.
Jack, who is a Hawaii native, was already on his way to the music festival to perform with ALO last night when he was asked to fill in for the English-folk rockers.
"I called my band and asked if they were up for it," Jack said in a released statement.
"Long story short – they are headed this way. I've got a lot of lyrics and chords to relearn by Saturday night. I was here to play the first Bonnaroo and it is a very special festival to my band. We are excited to hit the stage again."
Mumford & Sons have had to cancel six shows since Dwane was hospitalized last week but they reportedly hope to be back up and touring by the end of June.
We hope Ted has a healthy and full recovery!
And don't worry Bonnaroovians, we're sure Jack will rock like always and leave Mumford fans satisfied too. His performances are ALWAYS epic, we promise!
Get all of the Bonnaroo news you could possibly need and watch a live stream of the whole festival here on Cambio!