The former Tottenham star sealed a world-record €100 million move from White Hart Lane following a summer of endless speculation over his future.
The Wales international's agent, Jonathan Barnett, told The Daily Telegraph that the deal was the most rewarding that he has ever had to negotiate.
"I have been involved in some of the most difficult transfers you can possibly imagine over the years but this was the most rewarding one I have had the pleasure of negotiating," he wrote.
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"It's been intense, stressful and tiring and at times the negotiating was not always done in the most cordial way. There were times when we were worried Real Madrid could get frustrated and move on to other targets but I had to avoid having any negative thoughts.
"Did I ever fear it would get called off? No. Hand on heart, I always believed the deal would get done and I'm just so glad I was able to reward the trust that Gareth and his family placed in me."
Barnett also reserved praise for Spurs chairman Daniel Levy, explaining how he drove a hard bargain for the benefit of Tottenham.
"There have been ups and downs along the way and Daniel Levy has been hard and fair throughout the whole process," he continued.
"There are a lot of things said about Daniel, especially over the last few weeks, but he was always thinking of what was best for Tottenham and was determined to strike a deal that suited everybody."