Spain forward Jose Antonio Reyes has joined Atletico Madrid from Arsenal.
Winger Reyes has joined Real's city rivals
The 23-year-old signed a four-year deal for a reported £6m after Real Madrid refused to offer more than £4m.
Reyes, who spent last season on loan at Real and scored the vital goals against Mallorca to help the side to La Liga, said he was "happy" to return to Spain.
"I'm happy again at the club I wanted to join. Real wanted me right up until the last moment, but Atletico made a great effort to get me," said Reyes.
"The club have been interested in me a long time and tried to sign me from Sevilla when I was 13. I owe it to them."
Lyon also made a bid for Reyes, who cost Arsenal £10.5m when he arrived from Sevilla four years ago, but they all but admitted defeat after the player expressed his desire to play in Spain.
An Arsenal statement said: "Everyone at Arsenal thanks Jose Antonio for his contribution to the club and wishes him the best of luck for the future."
The winger was close to joining Atletico last summer, signing a pre-contract deal, before opting to join their city rivals.
"We had an agreement with him last year but Arsenal wanted to take Real's Julio Baptista on loan and there was no choice," said Atletico club president Enrique Cerezo.
"We have returned for the player once again and he wanted to come here."
The signing has split Atletico fans and Reyes admitted he was worried by the reaction, particularly as his first league outing for the club will be at the Bernabeu against Real.
"It will be a great game, the kind every player would want to play in," he said.
"I will have to prove my worth on the pitch, scoring goals, and by helping them to be successful."
Reyes, who has won 21 caps for Spain, made a total of 110 appearances for the Gunners and scored 23 goals.
He made 30 appearances with Real, mostly as a substitute, and scored six league goals.