The South Korean forward has completed a move from Spurs to MLS side LAFC and admits that it was extremely difficult to bid farewell to the Premier League club after 10 years in north London.
Son - who bowed out on a high by captaining Tottenham to Europa League glory last season - said in his farewell message: "It was probably one of the hardest decisions I ever made, so please don’t be disappointed. I will be disappointed not seeing you on the pitch.
"I will always be in your history books, and Spurs will always be in my heart, and Spurs will always be in my family.
"And as a kid, you welcomed me and as I grew up I’m leaving you, but there’s always good timing. I always wanted to leave in a perfect way, [so] that people can think about me in very proud moments and very happy moments. This is the right time to say goodbye."
Son is in fifth place on Spurs' list of all-time top goalscorers and has been hailed as one of the club's "greatest players" by chairman Daniel Levy.
He said: "Sonny is one of the greatest players to ever wear the famous Lilywhite shirt and he has been a joy to watch over the past decade.
"Not only is he a wonderfully gifted footballer, but he’s also an incredible human being who has touched hearts and inspired people throughout the club and all over the world.
"The Europa League triumph in Bilbao was a truly magical moment in the club’s history and Sonny lifting the trophy is a perfect lasting memory from his fantastic decade at Tottenham Hotspur.
"Sonny has given so much to this club, both on and off the pitch, and for that we are forever grateful. We wish him all the best for the future, and he will always be welcome back at the club as a beloved and cherished member of our Spurs family."