Real Zaragoza captain Gabi will return to Primera Liga rivals and boyhood club Atletico Madrid this summer.
The midfielder joined Zaragoza from Atletico in 2007 after three years as a senior player with Los Rojiblancos.
He played 142 games during his four-season stint at Zaragoza, the last two of which saw him wear the captain's armband.
Last season he scored 11 goals, including both in the club's final-day 2-1 victory at Levante as they finished two points above the relegation zone.
Speaking at a Zaragoza press conference, Gabi said: "I will always carry Zaragoza in my heart. I want to give thanks to everyone who has been so good during my time here, as much to me as my family.
"Real Zaragoza have made me regain my enthusiasm for football."