The 74-year-old actress - who won an Oscar for her portrayal of the monarch in the 2007 film The Queen - revealed that when she was invited to an intimate tea with her Majesty and Prince Philip, all she could do was talk “gobbledygook”.
Speaking at the ‘Helen Mirren and Hawk Koch Discuss The Magic of Movies’ event in New York this week, she recalled her “lesson in embarrassment” when she forgot royal protocol and couldn’t remember how to address the Duke of Edinburgh, 98, in order to ask him to “pass the milk”.
“She invited me for tea. I thought it was going to be in a room with 200 other people, which it often is,” the Hollywood star explained.
“I’ve met her once before and it was in a room with 200 other people.”
However, Helen - who did not specify when the meeting took place - was soon shocked to find she was one of just eight guests invited to the palace the Queen, 93, on this occasion.
“So I said, ‘Oh well I can manage that.’ So it was at the horsey place and the message came to me that the Queen would like to invite you to tea, she knows you’re here,” the actress continued.
“So I walk in, and there’s like eight people sitting around a table. Prince Philip, the Queen, a Sheik of somewhere or other and a couple of horsey people.
“I know absolutely nothing about horses, at all, and the Queen knows everything about horses.”
Helen admitted that she started to panic when realising she was struggling to contribute to the conversation.
She said that she was “desperately trying to make polite conversation and it’s just coming out like gobbledygook”.
The Academy Award-winner explained she was then handed a cup of tea while the monarch began to discuss the contents of the sandwiches in great detail.
Helen said: “Then I got a cup of tea and the Queen, in particular, was having a very intense conversation about what’s in the sandwiches with Prince Philip, very important. ‘What is this? What’s in here?’
“The milk is on the other side of Prince Philip and I want some milk in my tea, but my brain goes completely dead and I cannot remember how to address Prince Philip.
“I mean, is it sir? Is it your majesty? Is it your highness?
“Is it rude to ask him to pass the milk? Or should I just ask for a lackey?”
The star revealed that in the end she decided to not say anything and make do without milk.
She added: “I finished up not having any milk. I just couldn’t sort it out.
“It’s a lesson in embarrassment, but they were lovely, they were utterly gracious.”