Fortune won his place in the band in 2005 after triumphing on the talent show "Rock Star: INXS," but he was booted from the lineup in 2009 and forced to seek help for a substance abuse problem.
He was invited back to join the group as Michael Hutchence's permanent replacement in January, but the reunion didn't last, and he was not invited to join the group in the studio as they embarked on plans for their new music.
Now the remaining members of INXS have found a new frontman in singer Gribban, who provided backing vocals on Snow Patrol's "Eyes Open" track and wrote the tune "Celebration" for Madonna.
The singer says he cannot believe he's now fronting a band he used to idolize.
"Without a doubt I was a fan of INXS," Gribbin tells Billboard.com. "I remember 'Kick' like it was yesterday. I remember seeing the guys on MTV and then on Jools Holland's BBC show watching as a kid, just blown away by them. INXS definitely played a huge part in my musical education as a songwriter ... so to be in the band now is pretty amazing."
Gribban will hit the road with INXS for the first time in November with shows in Europe, Australia and South America.
Hutchence died in 1997.