Avram Grant described his decision to step down as Portsmouth manager last night "as one of the most difficult" of his career.
The Israeli won widespread praise for the way he led the club amid financial turmoil which resulted in administration, but was unable to save them from relegation from the Barclays Premier League.
His resignation has paved the way for him to become Gianfranco Zola's successor as West Ham boss.
Grant explained his decision to leave Pompey in an emotional open letter to fans on the club's official website.
"This was one of the most difficult decisions I've had to take in my football career. After a lot of soul searching and under the circumstances I'm taking a different direction," Grant said.
"It's been both a difficult and complex year for us at the club, but at the same time, it's been a wonderful and uplifting professional and personal experience.
"I have been inundated with letters and emails from fans. Many have brought tears to my eyes and take it from me; it takes a lot to do that. I will never forget you, the loyal fans of Pompey who, without a doubt, helped me protect the team under such complex circumstances.
"There are very few teams in the world that have fans as passionate and devoted as you are. Seeing you all so proud with your heads held up high is the best reward I can receive.
"It has been a great experience to be part of one of the most wonderful occurrences that has happened in the history of British football and also shows that even in the most desperate times, loyalty, devotion, professionalism and passion can be demonstrated. I wish you all the possible success which you genuinely deserve."
Grant's six-month stint in the Fratton Park hotseat was beset by off-field problems as the full scale of the club's financial trouble began to emerge. They went into administration in February and the following month were deducted nine points by the Premier League which all but condemned them to relegation.
He still managed to lead them to the FA Cup final, though, where they lost 1-0 to his former side Chelsea.
The Israeli's statement continued: "Portsmouth has given me a feeling of home away from home.
"I might be leaving Portsmouth physically, but you cannot take Portsmouth away from me and my heart.
"I have informed Andrew (Andronikou) the administrator that if and when the need arises, I will be at his disposal to assist in any way I possibly can."
Portsmouth's former chief executive Peter Storrie praised the work Grant did during a tough time at Fratton Park.
"He came to Portsmouth, fell in love with the club and did a magnificent job," Storrie, who stepped down in March, told Sky Sports News.