Dame Helen Mirren refused to take part in Queen Elizabeth II's Silver Jubilee celebrations in 1977 because she was a "grumpy anti-monarchist".
The veteran British star sneered at the parties marking the 25th anniversary of the royal's accession to the throne because she didn't approve of the aristocracy.
But the actress, who was made a Dame after winning an Oscar for playing the monarch in The Queen, now regrets boycotting the events.
She tells Woman & Home magazine, "At the time of the Silver Jubilee, I was a grumpy anti-monarchist. I didn't celebrate and was appalled by the celebrations. In my idiocy, I missed out. Actually a lot of the street parties people held looked great fun, so silly me."
Dame Helen is determined to embrace the Diamond Jubilee next month (Jun12) because she's amazed by the Queen's lengthy reign.
She adds, "I feel completely differently now compared with that time. At the Golden Jubilee (in 2002), I understood the amazing longevity of the Queen's reign and the importance of it. I really felt something extraordinary was unfolding - and now at 60 years, it's that much more... I feel kind of proud about this Jubilee. And actually immensely grateful that my life has had this one constant in it. I think the Jubilee is a very special and unique part of being British.
"She has stayed unbelievably consistent and followed a steady course. She's an incredible example to us because of that. Even now, at 86, there is no sign of the Queen diminishing at all in her role."