The 86-year-old, who will be replaced by Claudia Winkleman, has hosted the show since it began in 2004.
Speaking to The Sun, Forsyth said: "You do start to feel a bit stale, like a bit of fruit you've put in a bowl. You look at it one day and think, 'Oh - that's going off'.
"There are many reasons why I packed it in, but one was that I didn't want to do this series and suddenly in the middle of the show say, 'I can't do it any more'. I would have hated that."
Claiming to work as hard as the dancers, Forsyth said that he knew the previous series would be his last when it came to an end.
"I had to announce each couple, run upstairs for their dance, »
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