The Welsh winger completed a season-long transfer to former club Spurs after seven seasons at the Santiago Bernabeu, having joined Los Blancos in a £85m deal in the summer of 2013.
"Real Madrid C. F. and Tottenham Hotspur FC have agreed to the loan of Gareth Bale for next season, until 30 June, 2021," Madrid said on their website.
And with significant understatement, they added: "Our club wishes the best of luck to a player who is part of one of the most successful periods of our history."
Bale won 13 trophies as a Real Madrid player, including four Champions League crowns, scoring in the 2014 and 2018 finals and assisting Sergio Ramos in the 2016 showpiece.
The Welsh winger also hit the winner in the 2014 Copa del Rey final against Barcelona and netted over 100 goals in total as a Real Madrid player.