NEIL Harris says Millwall must embrace the task of rebuilding after they were relegated to League One.
Rotherham moved four points clear of the Lions with one game to play by beating Reading on Tuesday, a result which also condemned Wigan to the drop.
Harris, who took over from Ian Holloway on an interim basis in March, was yesterday confirmed as the club's permanent manager.
Millwall have lost just three of Harris' nine games in charge but the recent upturn in results and performances has not been enough to save them.
Speaking after the Lions' fate was sealed, Harris said: "At a difficult time for the club, we have to be disappointed but we cannot be despondent.
"There's frustration and disappointment but not despondency.
"We have to look immediately at our plans for next year and be as optimistic as we can be about rebuilding the squad and taking it in a different direction.
"There's an opportunity to sign new players and integrate more of our academy lads into the team.
"It's a big summer for the club and one that we must embrace. We have to look at this as a great chance to build a team similar to the promotion sides of 2001 and 2010.
"Where we go from here is very important – we have to recruit the right players of the right age and build on the last nine games.
"The fans have identified with a real Millwall team and that has to be the future for the club."
Chairman John Berylson he hopes Harris will reign at The Den for years to come.
"I want Neil to be our manager for a long time," he said. "He is very certain about what he wants for the future.
"I believe that Neil can recruit the right type of players, both young and old, because he's the sort of person that will appeal to good players.
"He was one himself and knows what it takes.
"He also recognises and respects quality. Neil has done a very good job and the question of when I would hire him has always been in the back of my mind."
Having invested heavily in Holloway, Berylson believes that a Millwall man such as Harris, despite his inexperience, could be a more natural fit for the club.
"You have to find someone special, have a bit of luck and get someone who can grow with you," he added.
"That's what Kenny Jackett did and that's hopefully what Neil will do. I don't think it's as simple as paying a manager £1million and getting guaranteed value for money.
"Prior to Tuesday, I knew that we had to rebuild whether it was in League One or the Championship.
"I'm tired of not winning and the last few years have been really hard for all of us. I recognise that we've struggled for too long so it is time to stand back and fix it."