Ross Barkley has signed for Chelsea from Everton, the Premier League champions have announced.
The 24-year-old's contract at Goodison Park was due to expire at the end of the season after he rejected a new deal with the Toffees.
A move to Chelsea on transfer deadline day in August did not materialise, but Barkley has now moved to Stamford Bridge for a cut-price fee, reported to be in the region of £15million.
Twenty-four-year-old Barkley has signed a five-and-a-half-year contract, which runs until 2023.
"I'm overwhelmed, I'm looking forward to it and I'm really excited to get started," Barkley told his new club's official website.
"To be given a fresh start at a new club like Chelsea, it's unbelievable for me. I'm looking forward to continuing where I left off at the end of last season and hoping to improve and add more goals to my game."
Director Marina Granovskaia added: 'Ross is a player we have long admired and are certain he will prove to be an important player for Chelsea.
"He possesses outstanding technical and physical attributes, matched with good experience of the Premier League and a strong desire to succeed at the highest level. We welcome him to the club and look forward to seeing him in action.'
Barkley has yet to play this season due to a hamstring injury, but he is nearing match fitness.
And Antonio Conte believes the midfielder is a sound investment for the Blues.
Speaking ahead of Chelsea's FA Cup third round tie at Norwich on Saturday and prior to the deal being confirmed, Conte said: "We are talking about an English player, a young player. He has good prospects for Chelsea. I think the club decided for this investment also for his contract.
"I think this is a good opportunity for the club to buy this player.
"For sure he is a good prospect for Chelsea."
May's loss to Arsenal was the last Toffees appearance for the Everton academy graduate, who made 150 Premier League appearances for Everton, scoring 21 goals.
Conte urged caution over expectations for Barkley.
The Italian added: "Don't forget he had a bad injury, he had surgery. This player has not played in seven months.
"We must have great patience. We have to hope to recover him very quickly, to try to help us for the rest of the season."
Conte declined to address rumours West Ham striker Andy Carroll was a target, saying transfers were not his remit.
He added: "The recruitment is not my job. The club try to do the best for this team, to try to improve this team."