The 21-year-old has agreed a deal with Barcelona to move to the Camp Nou this summer, but he could have been with the Lilywhites this season had he accepted their offer.
De Jong told FourFourTwo (h/t Mundo Deportivo, via Football Espana) why he chose not to join Spurs:
"It was not the right moment. I was injured and I thought 'not yet,' I felt that I had to stay at least one more year in Ajax.
"I considered the offer long and hard. It's a very stable club, and it's going to be better. They also have a manager, Mauricio Pochettino, who is committed to young people and makes them better.
"I like the kind of game they play with, and I think it would have been right for my game.
"I always wanted to play in Barcelona and the amount they were willing to pay to Ajax for me showed me this seriousness. I felt I had to take the opportunity because I would not have it again."
Tottenham have a strong relationship with Ajax, from whom they signed Christian Eriksen, Toby Alderweireld, Jan Vertonghen and Davinson Sanchez.
Pochettino has also helped develop the likes of Harry Kane and Dele Alli from younger players into first-team stars, so it's easy to see why De Jong considered the move.
Having failed to sign De Jong or any other targets, Spurs finished the 2018 summer transfer window without a single acquisition.
Victor Wanyama has been injured for much of the campaign and Mousa Dembele was allowed to leave in January, which has made their failure to reinforce even more costly.
Left-back Danny Rose finished Spurs' 1-1 draw with Arsenal on March 2 in midfield, much to the frustration of the Evening Standard's Dan Kilpatrick and WhoScored.com's Ben McAleer:
De Jong in particular could have been a fine addition to their team, as he's a highly promising talent.
Football statistician Dave O'Brien and Dutch football writer Sjors van Veen singled him out for his role in Ajax's recent 3-1 win over Eredivisie title rivals PSV Eindhoven:
While he's still only 21, he looks ready to slot into Barcelona's midfield with ease upon his arrival in the summer.
Spurs have been left to rue their failure to prise him away from Ajax last year, and they'll need to concentrate their efforts this summer on improving their central-midfield options.