The Tottenham striker handed in a transfer request shortly after the club went down to the Championship a decade ago, and left for the first of two spells at White Hart Lane in January 2004.
The timing of his request drew criticism from West Ham fans, and the 31-year-old has now said he handled his departure from Upton Park poorly, citing bad advice from his then-representative as a factor.
"It was a massive mistake. I didn’t really want to do it," Defoe told ITV4's Sports Life Stories.
"We're talking about leaving the club I was in love with at the time because I came through the youth system with my friends, the fans loved me there. They were brilliant - every game they sang my name.
"The person who represented me at the time said, 'You need to hand in a transfer request and get in early because all the lads are going to leave'.
"The backlash was crazy. I felt like I was on my own and people were absolutely abusing me.
"To this day I can imagine West Ham fans look at me and think, 'Who does he think he is? How can you do that? You're a Judas'. And it’s quite sad really because I can honestly say I still love that club."
Defoe's future is reported to be uncertain, with Tottenham manager Andre Villas-Boas preferring Roberto Soldado in the lone striker position at White Hart Lane.
Were he to leave in the January transfer window, he would so without having won a major trophy at the club - something he says would be a big regret.
"I think especially playing for a top club, a club where you should win trophies it would be disappointing," he continued.
"At the end of your career you want to sit back and say I won this or I won that because that’s what it’s all about. You want to win things and you want to be the best.
"Spurs is a great club with a great history. That is why this year is a big year. I believe we can win something and I believe that once the first one comes, more come after that."
