Chelsea have signed Barcelona B midfielder Oriol Romeu on a four-year contract for €5 million.
Oriol, 19, will link up with the Chelsea squad following the World Under-20 Championships in Colombia.
Barcelona have included a buy-back clause of €10 million after one year, which will rise to €15 million after the second year.
He is the first player new boss Andre Villas-Boas has brought in for the 2011-12 campaign, after goalkeeper Thibaut Courtois was loaned to Atletico Madrid following his arrival from Genk.
Oriol began his career with Espanyol before switching to Barca's Academy in 2004. His La Liga debut came as a substitute in a 0-0 draw against Deportivo La Coruna towards the end of last season.
Oriol is a tough-tackling midfielder in the mould of Sergio Busquets and he is also capable of playing in the centre of defence.
He told AS earlier this week: "Chelsea is a great option for me. If everything goes well, why not? Leaving Barca hurts, but you have to take your chances."