Aiden O'Brien has left Millwall after his contract expired.
The attacker made 226 appearances for The Lions between 2011-2020, scoring 44 goals.
After making his way through the youth ranks in SE16, Kenny Jackett was to hand a fresh-faced O'Brien his competitive debut in a Carling Cup outing at Wolverhampton Wanderers on 20th September 2011.
Loan spells to Hayes & Yeading, Crawley Town, Aldershot and Torquay United followed, before the Irishman began to become a more permanent fixture during the 2014/15 campaign, making 20 appearances and scoring his first senior goal in a 2-2 draw at Brentford. O'Brien doubled his tally on the final day at Wolves.
If 2014/15 was considering Aiden's breakthrough season, then 2015/16 was the year in which the frontman stamped his mark on Millwall's side. The Lions had their hearts broken with a League One Play-Off Final defeat to Barnsley at Wembley Stadium, but O'Brien played 53 times in a marathon season, scoring 13 goals, including a first senior hat-trick at Crewe Alexandra and a double at high-flying Sheffield United.
Alongside Lee Gregory and Steve Morison, O'Brien formed the third part of a lethal trio who would score 111 times between them in two seasons, and 15 of those were to come through the Irishman in 2016/17, as Millwall banished the demons of 12 months previous to win the League One Play-Off Final at the expense of Bradford City.
The eighth of those 15 strikes provided O'Brien - and a few hundred hardy souls - with one of the most memorable moments of his career. With The Lions 2-0 down on a half-frozen pitch at Gigg Lane, the home of Bury, Shaun Williams' 70th-minute penalty and Calum Butcher's equaliser four minutes from time looked to have earned Millwall a share of the spoils, but in stoppage-time, the striker popped up with a close-range finish to spark wild celebrations amongst the away section in Lancashire. Not content with celebrating on the pitch, O'Brien took it upon himself to leap into the stands and rejoice with those who had made the long journey.
Now a Championship footballer, O'Brien made 32 appearances and scored six goals as Millwall enjoyed a healthy first season back in the second tier, finishing eighth. His most unforgettable strike that season came on 16th September, as he scored the only goal to lift the roof off The Den and hand a first defeat of the campaign to Leeds United.
The attacker was to also find the net in the reverse fixture, as Neil Harris' side completed an outstanding 4-3 victory at Elland Road.
An established starter in Millwall's XI, international football came calling for O'Brien in September 2018 - and he marked that achievement with a goal, heading home in a 1-1 friendly draw in Poland. Three Nations League caps and a European Championship Qualifier at home to Georgia followed, but back in SE16, O'Brien was raising the roof once more as put The Lions 2-0 up in an FA Cup Quarter-Final against Brighton & Hove Albion.
Aiden's last Millwall goal came on 29th December 2019 when Brentford were defeated 1-0, and his last appearance was on 29th February in a 1-1 draw with Bristol City. But, off the pitch, O'Brien offered so much more to the club, with his work in the community recognised with the 2019/20 PFA Community Champion award.
The club would like to thank Aiden for his sterling work on and off the pitch during his time with the club and wish him the very best for the future.