The 44-year-old former Addicks full-back was axed by owner Roland Duchatelet on Tuesday after a disagreement over the club's recruitment policy and replaced by little-known Belgian coach Jose Riga.
Despite their position at the foot of the Sky Bet Championship, Charlton fans showed their backing for Powell by applauding and chanting his name after three minutes of Wednesday's 0-0 draw with Huddersfield, a reference to his shirt number as a player.
And in a statement issued via the League Managers' Association, Powell said: "Following my sacking, the first thing I want to do is give my most sincere thanks to the superb Charlton Athletic fans for their continued and unconditional support.
"I have always maintained a wonderful relationship with them both as manager of the club and during my three different spells as a player.
"I always said I would never walk away from this great club and ultimately it's not about individuals, it's about the club and our fantastic supporters.
"I have over 15 years' association with Charlton dating back to 1998, and over the years I have enjoyed many truly wonderful times.
"So, it is with deepest regret that my time as manager has now come to an end.
"It was an honour to have been given the opportunity to manage the club and without doubt the proudest moment of my career in football was leading Charlton to the League One title, amassing 101 points in the process - a club-record points tally.
"On a personal note I was extremely privileged to have been voted by my peers as the League One Manager of the Year following the success we all enjoyed.
"We experienced a fantastic first season back in the Championship by finishing ninth last term and I was confident that we would have secured our Championship status once again this campaign.
"In closing I simply want to wish everyone connected with Charlton Athletic the very best for the future."