At a media conference in Seoul on Saturday, Son said his decision to leave was the most difficult of his career and the club was supporting him as he looked to move on.
Spurs will face Newcastle United in a preseason friendly on Sunday in Seoul in what could the final match of Son's time at Spurs.
"Before we start the press conference, I just want to share the information that I have decided to leave this club in this summer," Son said.
"Respectfully, this club is helping me to my decisions. So I just wanted to share this information before we start the conference."
"I came to North London as a kid, 23 years old, very young age, a young boy came to London who even didn't speak English and leaving this club as a grown man is a very, very proud moment."
Son also paid tribute to Tottenham fans.
"I just want to say thank you to all of the Spurs fans that gave me so much love and felt like it was my home," he said.
"It was one of the toughest decisions I ever made. So I hope the goodbye is always also in a good timing you know.Â
"But I think it's the right time to make this decision. So I hope that everybody understands my decision and hope that everyone respects that."
Son said he did not have an answer about his playing future though he plans to play for South Korea at next year's World Cup in North America.
Media reports have also suggested MLS outfit Los Angeles FC are among favourites to secure his signature.
Son achieved his goal of silverware in May when he helped Spurs to Europa League success with a 1-0 victory over Manchester United.
It ended a 17-year trophy drought for the club, though the win failed to save the job of Postecoglou who was promptly replaced by Thomas Frank.
In 454 appearances for Tottenham, Son scored 173 goals.
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