"I have had an absolutely brilliant time on Coronation Street," said John in behind-the-scenes footage.
"I have loved playing Karl, it is always more interesting to play a character who has a flaw, and Karl has many flaws.
"He is addicted to gambling, he has got as bit of a drink addiction and he is also addicted to women.
"Those three things create a wonderful character to play. I will really miss getting inside the head of Karl Munroe.
"From an acting point of view, one of the highlights was obviously when Karl set fire to the Rovers - one of the most iconic pubs in Great Britain, which was amazing."
For months viewers have watched as Karl plotted and schemed to ensure the truth was not uncovered.
But unfortunately for Karl, he could do nothing to calm the suspicions of Sunita's widower Dev.
The drama came to a head when Dev blasted into Karl's wedding to Stella Price, albeit slightly late, to tell Karl's new wife what he knew.
"I thought it was a great ending," said John.
"I thought it was good that Stella convinced Karl to be the man that she once knew and he was to be honest with himself, admit that he was wrong and admit that he had killed.
"To walk out and say: "OK guys, hands up - yeah, I did it" and he kind of absolved himself in as much as you can do, having been the cause of two people's death.
"Is this the last we will see of Karl? Well he's alive, he is inside and he is doing time. Who knows?"