Patrick Vieira's nine-year spell at Arsenal is over, after he completed a £13.75m transfer to Juventus.
Vieira signed a five-year contract with Juve on Friday after finalising personal terms and passing a medical.
The 29-year-old Frenchman returns to Serie A where he played for AC Milan before joining Arsenal in 1995.
"It was a very difficult decision, but I am happy with it," said Vieira, who was unveiled at a media conference, wearing a Juve top, on Friday.
The two clubs confirmed on Thursday they had agreed a fee of 20m euros (£13.75m) for Vieira, who almost joined Real Madrid for £23m last summer only to have a last-minute change of heart.
And Juve general manager Luciano Moggi claimed that they beat the Spanish giants to the Frenchman's signature this summer too.
"We were up against Real Madrid, which did everything to grab him," said Moggi.
Reports in Italy suggest Juventus will pay an initial instalment of £6.88m, with payments of £3.44m to follow in July 2006 and July 2007.
"Juventus will unveil new signing Patrick Vieira at noon (Central European Standard Time) on Friday at the club's headquarters in Turin," said a statement on the Italian club's website.
Joined Arsenal: Aug 1996 (Arsene Wenger's first signing)
Made captain: June 2002
Premiership titles: 3
FA Cup medals: 4
Red cards: 10
The man who signed Vieira for Milan as a teenager from Cannes - Fabio Capello - is the same coach who has now taken him to Juve.
"Vieira is a very important player," said Capello.
"At the heart of midfield, his presence is felt not only for his technical value but for his physical quality.
"Vieira brings something extra that new signings have to bring."
The Frenchman only made two league appearances under Capello at the San Siro.
Capello said: "He was young and his path was blocked by (Marcel) Desailly and (Demetrio) Albertini back then.
"But you could already see that he had quality, otherwise I wouldn't have considered him as (Frank) Rijkaard's heir."
Arsene Wenger, who took him from Milan as his first signing for the Gunners, said: "I share the sadness with our supporters that Patrick has left us.
"But on the other hand I would say to them 'trust us and support us'. The sad thing is he leaves us, but the good thing is that he leaves us on a high.
"Patrick was a great player for us, one of the greatest in the club's history and I feel I had a special relationship with him because I made him come here.
"I think his impact, not only at Arsenal but in English football overall, was just tremendous."
Vieira added: "When you spend nine years at the club, like I did, it is a difficult decision to leave.
"But in the end you have to make a choice for your future. It was a very difficult decision, but I am happy with it.
"I made the decision to leave because I felt it was time for me to have a new challenge. But that does not mean I was unhappy or that I was having a problem at Arsenal.
"It was just that I had the feeling I needed to grow and meet a new challenge, and I feel Juventus was the best challenge for me.
"I'd like to thank the Arsenal fans. They have been fabulous.
"Even recently in the street they were saying 'if you are going, then thanks for the last nine years'. That is really touching and it makes me feel that I gave my best for the club.
"I can go with my head held high. I did my best every day in training and in every match, and I left shaking the hand of Arsene Wenger and Mr (David) Dein. That was really important to me."
Vieira's last game was the FA Cup final, when he lifted the trophy after beating Manchester United on penalties.
Now Gunners supporters will be waiting to see who Wenger buys to replace the Highbury captain, amid reports that Arsenal planned to sell Vieira in order to finance their summer spending plans.
Reports in Friday's newspapers have suggested Newcastle's Jermaine Jenas is Wenger's main target, possibly with a deal including the transfer of Sol Campbell to St James' Park.
England midfielder Jenas, who joined Newcastle from Nottingham Forest in 2002 for £5m, is apparently seen as the ideal replacement for Vieira, and is the right age at 22.
Campbell, who will be 31 in September, lost his place in the Gunners defence last season, with Wenger preferring a partnership of Kolo Toure and Philippe Senderos.