Alvaro Morata has joined Atletico Madrid on an 18-month loan deal from Chelsea.
Morata completed his medical with Atletico on Sunday before finalising a deal to take him back to the club where he started his youth career.
Atletico are scheduled to face two of Morata's former clubs in the next month - with games against Real Madrid (February 9 - La Liga) and Juventus (February 20 - Champions League).
Morata joined Chelsea from Real on a five-year contract for a then-club-record £57m fee in July 2017, while Antonio Conte was in charge.
He scored seven goals in his first eight games for the club, but finished his first season at Stamford Bridge with just 11 Premier League goals.
Head coach Maurizio Sarri was keen to offload the forward having preferred to play Eden Hazard in an advanced role.
Morata's loan switch also comes after Gonzalo Higuain joined Chelsea on loan from Juventus for the remainder of the season.
Chelsea have the option to extend the loan deal for a season or buy Higuain outright for £31m, according to Juventus.
The 31-year-old striker worked under Sarri during his spell at Napoli.
Morata will join former Chelsea striker Diego Costa at Atletico, who sit second in La Liga.