Chelsea have signed Borussia Dortmund forward Christian Pulisic for £57.6m, with the American international being loaned back to the German club for the remainder of the season.
The 20-year-old has become Chelsea's second most expensive outfield player of all-time, after Alvaro Morata.
"In the summer of 2019; I move onto Chelsea and to a new competition, the English Premier League," Pulisic said. "It's a privilege to have signed for such a legendary club and I look forward to working hard towards being a contributor to their team of world-class players.
"(I'm) looking forward to working with Maurizio Sarri and his technical team. But for six months, it's all BVB (Borussia Dortmund)!
"Please do not doubt my passion, determination and my 110 per cent commitment to the team right until the last ball is kicked this season."
Pulisic broke into the first-team at Dortmund during the 2015/16 season, and has scored 15 goals in 114 games ever since.
Dortmund sporting director Michael Zorc says the Bundesliga leaders tried to persuade Pulisic to sign a contract extension, with his deal expiring in 2020.
"It was always Christian's big dream to play in the Premier League," Zorc admitted. "It certainly has to do with his American background and as a consequence, we were unable to extend his contract.
"Given that his contract runs out soon, we have now decided to accept the extremely lucrative offer from Chelsea."