Ukraine international Andriy Shevchenko has completed his move to AC Milan from Chelsea after passing a medical.
The 31-year-old spent two seasons in west London after signing from Milan for about £30m in 2006, but has failed to make an impact at Stamford Bridge.
"I'm so very happy to be here," he told the Italian club's official website.
"At this special moment, I want to send a message to the Chelsea fans who have always made me feel their support. A heartfelt thank you for that."
Shevchenko, AC Milan's second-most prolific goalscorer of all-time, with 127 goals from 208 games, was unable to hold down a regular spot at Chelsea, scoring only nine goals in his 47 Premier League appearances, but maintains he enjoyed his time at the club.
"It was unfortunate I suffered a number of injuries during my time here but I always gave my all, whatever the circumstances", he said.
"I really have enjoyed playing in England and have made many friendships that will stay with me forever.
"I will always look back with fond memories of my time at this really great club, and I would also like to express my gratitude to Roman Abramovich for all his help and encouragement."
Despite his lack of success at Chelsea, Shevchenko has always been held in high regard by Milan's fans and staff.
Milan vice-president Adriano Galliani has expressed his joy at seeing the striker back at the San Siro and insists his return was not solely down to the club's owner Silvio Berlusconi.
"Andriy made a mistake in leaving and I think after two years he has understood that this is his home"
"It's not true that only Silvio Berlusconi insisted that Andriy return. I've put my weight behind the cause too and I'm happy that in the end we've succeeded in bringing him home."
He added: "After a series of frenetic phone calls during the whole day, we reached an agreement with Chelsea.
"We have managed to bring home a player who has scored the most goals in our shirt in the last 50 years."
Shevchenko's first season at Stamford Bridge ended prematurely when he had hernia surgery, forcing the striker to miss the Champions League semi-final against Liverpool and the FA Cup final.
New Chelsea coach Luiz Felipe Scolari did not pick him for their first Premier League match of the campaign last weekend, prompting Milan to launch the latest in a string of attempts to re-sign the player.
AS Roma and Sampdoria also expressed an interest but returning to Milan was always Shevchenko's preferred choice.
"For me, it's like winning the Champions League," Shevchenko told Italy's ANSA news agency. "There were complications but now everything is resolved I'm really happy."
606: DEBATE
The details of their eventual agreement remain confidential.
After buying Brazil playmaker Ronaldinho from Barcelona at the start of the close season, Milan had said they would not bring in any more players.
However, an injury to Marco Borriello, Alexandre Pato's stuttering form for Brazil at the Olympics and Filippo Inzaghi turning 35 have made the signing of another striker necessary.
"I have heard from Andriy about 48 times in the last three hours. Andriy made a mistake in leaving and I think after two years he has understood that this is his home," added Galliani.
"Now he has made economic sacrifices but at this point what counts is that he has come back to us."
Shevchenko began his career at Dynamo Kiev, winning five league titles and two national cups with the team between 1994-99.
He spent seven successful years at Milan, helping the Rossoneri clinch the 2002/03 Champions League 2003/04 Serie A title.
He was also named European Footballer of the Year in 2004.
However, he missed the penalty that gave Liverpool victory in the 2004/05 Champions League final.
The Serie A season kicks off on 31 August, with Milan set to play host to Bologna in their opening game.
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