Chelsea have loaned midfielder Saul Niguez for the season to Atletico Madrid.
Saul will join Chelsea for an initial £ 3.4million (€ 4million) fee, with the Blues given the option to make the deal permanent for £ 30million (€ 35million) in the summer next.
The 26-year-old, who was part of Diego Simeone’s title-winning squad last season, has made more than 300 appearances for Atletico after making his first-team debut at 17 in 2012.
Saul told the Chelsea website: “I am very happy to start this new challenge with Chelsea.
“Blues fans, I’m one of you now and I can’t wait to put on the jersey, start training and see you all. Goodbye !
Chelsea manager Marina Granovskaia added: “We welcome Saul to the club and believe he completes our squad as we compete for top honors in five different competitions this season.
“He is a proven winner, a player with a lot of experience and we know he will be very well suited to the challenges that lie ahead on all fronts over the coming year.”
In addition to winning La Liga last season, Saul also won two Europa League titles and the Copa del Rey during his time at Atletico.
The 26-year-old has 19 caps for Spain, although he hasn’t played for his country in almost two years.
Saul’s arrival was confirmed after the Premier League transfer window closed at 11 p.m. Tuesday night, but was allowed to proceed as the documents were submitted on time.
He is Chelsea’s third and final signing this summer, following the arrival of third-choice goalkeeper Marcus Bettinelli from Fulham and the purchase of the club record from Inter Milan striker Romelu Lukaku.
However, the Blues were unable to close the signing of Sevilla defender Jules Kounde after La Liga imposed a price tag of almost € 80million (£ 68.7million) internationally. French.
Koundé was keen to join Chelsea, but the European champions did not increase their bid by around € 50million (£ 42.9million).