The actor revealed the news during an appearance on ITV1's Magic Numbers, following an admission from producer Phil Collinson in June that he was considering staging a live episode.
Host Stephen Mulhern asked: "Is it true that they are definitely going to do a live episode to celebrate the 50th [anniversary]?"
Duffy replied: "I don't know if I'm allowed to tell you this, but yes, they are!"
Earlier this month, The People reported that producers were planning a live episode which would focus on the aftermath of the forthcoming tram crash stunt.
Speaking at the time, a source said: "There's a real buzz around the live episode. Everyone wants things to go off without a single cock-up - no messed-up line or moving dead body."
The show celebrates its 50th birthday in December.