Thousands of fans crowded New York's Times Square to help bid a fond farewell to the cast.
"It is really crazy, I mean, these people are so enthusiastic, especially in America, I find they're even crazier," said Grint.
"It's been the most amazing rollercoaster ride and what an amazing companion I had for the journey," Watson said. "Hermione is such an easy role to have played and to get to walk around in her shoes is really something."
In "Harry Potter and the Deathly Hallows: Part 2," the eighth and final installment in the series, Harry, Ron and Hermione have one last bid to get rid of Lord Voldemort. The "Harry Potter" movies have become one of the most successful film franchises in history, and successful cinema often lives on.
"There is a generation of kids who will then introduce their kids to it and I think it will just keep perpetuating itself as we grow up and pass it on," Radcliffe said.
Watson said the final film is a classic.
"The themes that it touches on are timeless and universal," she said. "I just don't think - it's the end, but I don't think it is, really."
The stars have been part of the Potter phenomenon for more than 10 years. Watson says growing up with her Potter pals has taught her a lot, not just about acting, but also about life.
"Nothing will ever be as difficult as this has been. In a good way, in a nice way," she said. "It's just that I'm so grateful that I learned so much and that I've had so much experience and that I can go into other things feeling pretty confident that there's basically nothing that they can throw at me that will be too alarming."
"Harry Potter and the Deathly Hallows: Part 2" will be in theatres a minute after midnight Friday. The franchise's finale is expected to be the biggest movie of the summer.