THREE DAYS GRACE lead singer Adam Gontier has quit the band due to an undisclosed health issue.

The Canadian melodic rockers have announced that My Darkest Days frontman Matt Walst will be joining the group as their singer for their upcoming North American tour.

Gontier co-founded THREE DAYS GRACE in 1997 and the band went on to release four successful studio albums with him in the singer's seat.

Here is a statement from THREE DAYS GRACE bassist Brad Walst (who is also the older brother of Matt Walst):

"We were surprised and distressed by Adam's sudden departure. We are however very excited for this upcoming tour, and to have my brother Matt stepping in as lead singer."

THREE DAYS GRACE recently issued Transit of Venus, which debuted #5 on the Billboard Top 200 Album Chart, upon its release in October.

The 2nd single from the album, 'High Road,' goes to radio Jan. 22.

 The band begins a co-headline tour with SHINEDOWN and special guest P.O.D, kicking off on Feb. 1 at the iWireless Center in Moline, Ill.