Day 26 -- BOY BAND REUNITING -- And We Have Diddy's Blessing

Day 26 -- the boy band masterminded by Sean "Diddy" Combs on MTV's "Making the Band 4" -- IS TOTALLY REUNITING FOR A NEW TOUR ... TMZ has learned.

A rep for Day 26 tells us ... the band, which was handpicked by Diddy on the 2007 show, is planning a 30-city tour starting in the Spring of 2014 ... and it's gonna include ALL of the original members.

Back in the day, D26 produced 2 albums before trouble began. Qwanell "Que" Mosley was kicked out of the group in 2009 because of disagreements with management.

The whole band broke up in the summer of 2012 ... and there've been rumors of a reunion ever since. It wasn't until Que climbed on board that it became a reality.

As for Diddy ... we're told he's NOT part of the resurrected band ... but he's already given the boys his blessing.