Isaacs, who plays Lucius Malfoy, admitted that he loves being part of everything Harry Potter-related and is delighted with the treatment the movies have received.
"I always get upset when I hear it called a franchise, because that's when someone sells burgers," he said. "This is a series. This is one story, essentially, that's taken ten years to tell so beautifully and with such care.
"It seems to me there's not a drop of cynicism in anybody's participation."
Coltrane agreed with Isaacs and added: "It really p*sses me off if you're talking about a franchise. This is about seven years in the boy's life, and that's the way we should see it.
"We're all emotionally tied into it, I have to say. We were all terribly sad when it was over."
Watch Jason Isaacs and Robbie Coltrane at the Harry Potter and the Deathly Hallows: Part 2 London press conference below:
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Watch Hollywood stars such as Tom Hanks, Vanessa Hudgens, Ryan Reynolds and Russell Brand offer their thoughts on the release of the final Harry Potter film below:
Additional reporting by Simon Reynolds.