The Welsh winger, who became the world's most expensive footballer when he moved from Spurs to the Bernabeu last month, describes the lure of playing for the La Liga giants as too good to ignore.
When asked if he would have stayed at White Hart Lane if Spurs had qualified for the Champions League last season, Bale replied: "It's once in a lifetime and I don't think you can turn down a team like that.
"For me I want to be playing in the Champions League, but also winning trophies. At a club like that they're out to win every trophy they're involved in. That's exactly what I want to do.
"When Real Madrid comes in it's a once in a lifetime opportunity. I think if I didn't take it I would probably regret it for the rest of my life."
Bale is expected to make his debut for Madrid at Villarreal one week today.