His decision came after a week when The Lions' Trust gave him a vote of no confidence and a 1-1 draw against Plymouth Argyle which all but confirmed Millwall's relegation to League One, just two years after appearing in the FA Cup Final.
"It's finished now, and we are relegated," he told journalists after the game. "The task now is to prepare for next season and League One.
"Someone will have to prepare for the new season but I definitely won't be the manager, that was always the case.
"We always knew a new man would come in and he'll now have to take the club back where they belong."
Many fans will argue that the club shouldn't have been allowed to slip away in such a shameful fashion, but having enjoyed a successful start to his managerial career at Christmas, the board decided to give Tuttle until the end of the season to keep The Lions up.
That decision has now come back to haunt them after a string of poor results, including defeats at home to Leicester City, Brighton & Hove Albion and Sheffield Wednesday.
Yet despite that run, Tuttle seemed to indicate that he wasn't willing to vacate the manager's chair so soon and wanted the job on a permanent basis. That no longer appears to be the case.
"My position will be spoken about, but the club is the important thing. Everyone needs to look themselves in the eye.
"It's sad a club like Millwall will be fighting in League One, but we need to be prepared as we can't afford to drop through another division."