Jose Mourinho has been confirmed as Chelsea's manager, returning for a second stint in charge at the club.
Mourinho, 50, replaces Rafael Benitez after leaving Real Madrid, and has signed a four-year contract.
The Portuguese won two consecutive Premier League titles during his first spell, which ended in September 2007.
Mourinho told Chelsea TV: "I promise exactly the same things I promised in 2004, with this difference to help - which is I'm one of you."
He added: "In football, in my career I've had two great passions, Inter and Chelsea, and Chelsea is more than important for me.
"It was very, very hard to play against Chelsea and I did it only twice, which was not so bad."
Mourinho, who will be officially presented in a press conference at Stamford Bridge next Monday, 10 June, brings three coaching staff with him in Rui Faria, Silvino Louro and Jose Morais.
Chief executive Ron Gourlay said of Mourinho: "He was and remains a hugely popular figure at the club and everyone here looks forward to working with him again."
Mourinho first arrived at Stamford Bridge in the summer of 2004, weeks after guiding Porto to the Champions League trophy.
He won the FA Cup and two League Cups as well as two Premier League titles but could not win the Champions League with the Blues.
His relationship with owner Roman Abramovich grew increasingly troubled and he quit despite having three years left on his contract.
Gourlay added: "I am delighted to welcome Jose back to Chelsea. His continued success, drive and ambition made him the outstanding candidate.
"It is our aim to keep the club moving forward to achieve greater success in the future and Jose is our number one choice as we believe he is the right manager to do just that."
He won his second Champions League trophy with Inter Milan in 2010, but left to join Real Madrid later that summer - replacing Manuel Pellegrini, who is favourite to take over at Manchester City.
He finished second in La Liga in his first season - four points behind Barcelona - but won the title a year later, amassing 100 points in the process.
However, this season Mourinho has cast a sulky figure, rowing with established players such as Iker Casillas, Sergio Ramos and Pepe, while seeing Barca romp to the title.
"I know in England I am loved," he said after Real's Champions League exit to Borussia Dortmund in April. "I know I am loved by some clubs, especially one."
Mourinho will return to a squad which contains some familiar faces, with Petr Cech, Ashley Cole, Frank Lampard, John Mikel Obi and John Terry still regulars, while Michael Essien also remain on the books.
Lampard told BBC Sport: "He's a great manager, I've said it a million times to the point of boring people, but I'm very fortunate to have worked under him before.
"He took my game on a million miles, and my personality in terms of football on a million miles. A lot of the reasons I moved on in the game is because of him.
"He's taken that (a winning mentality) everywhere he's gone with him. He creates a spirit in his squads that you can see from the outside is very, very strong. He's a top-class manager, we all know that."
Mourinho replaces Benitez, who was brought in on an interim basisto take over from Roberto Di Matteo in November and left to join Napoliafter securing third place in the Premier League and winning the Europa League.
Chelsea managers under Roman Abramovich
· Claudio Ranieri: Sep 2000 to May 2004
· Jose Mourinho: Jun 2004 to Sep 2007
· Avram Grant: Sep 2007 to May 2008
· Luiz Felipe Scolari: Jul 2008 to Feb 2009
· Guus Hiddink: Feb 2009 to May 2009
· Carlo Ancelotti: Jun 2009 to May 2011
· Andre Villas-Boas: Jun 2011 to Mar 2012
· Roberto Di Matteo: Mar 2012 to Nov 2012
· Rafael Benitez: Nov 2012 to May 2013
· Jose Mourinho: June 2013 -