Millwall's Under 18s and Under 23s have been awarded their respective divisional titles via the points-per-game method.
The Academy season was curtailed in April as the COVID-19 pandemic swept across the country, with both Professional Development League campaigns coming to an abrupt end, but both young Lions sides, who were battling at the top before lockdown, have been named as champions.
The Under 23s, managed by Kevin Nugent, were enjoying a rich run of form and finished their season unbeaten in nine matches. That run included an impressive 1-0 victory over a Crystal Palace side possessing Premier League experience, as well as a 2-0 victory at another local rival in Charlton Athletic.
The Under 18s, meanwhile, enjoyed a successful League campaign under the guidance of Larry McAvoy and Chris Perry, also memorably reaching the Quarter-Finals of the FA Youth Cup before being narrowly defeated by Chelsea at Stamford Bridge. The free-scoring youngsters hit an incredible 61 goals in just 19 League matches to top the table.
Scott Fitzgerald, Millwall's Academy Director, said: "Naturally I'm delighted and want to praise everybody involved throughout the Academy set-up.
"This is a brilliant achievement for the season but the reality is it is the culmination of several years of hard work. Some of these players have been with us since the age of nine and come right the way through the Academy, so you have to credit not just them but also their coaches and support staff who have each made an impact on their development and progress.
"It's brilliant to win the two Leagues but most importantly for us it's about getting players coming through the Academy, into the first team and then playing regularly. Billy Mitchell has featured 10 times so far and there's also been debuts for the likes of Hayden Muller and Tyler Burey recently.
"We need to continue working harder than ever to make sure as many of our homegrown players are following suit into next season and beyond."
"It's so pleasing to win the League for the first time," Nugent added.
"The lads deserve tremendous credit for their efforts throughout the season and I couldn't be happier for them that they've been rewarded with a League title to their names.
"We work for a football club which is very well managed from top to bottom and that translates out onto the pitch at all levels. We've managed to retain the majority of players who have contributed to this success which is credit to the chairman and the board and I'd like to extend my thanks to all of the staff involved, not just with the U23s but throughout the first team and Academy. Everyone has played their part."
McAvoy said: "It's a brilliant achievement and something which all of the players and staff can be very proud of.
"There has been so many high moments and everyone can look back with fond memories of the season and what has been achieved.
"It wouldn't have been possible without the hard work carried out day after day, week after week, throughout all levels in the Academy and across all departments."