When the 89-year-old monarch settles in to watch the hit show, she does so with a keener eye than most
Credit: Getty

Trust us, Lady Mary maniacs: You don’t know Downton Abbey like Queen Elizabeth knows Downton Abbey.

When the 89-year-old monarch settles in to watch the hit show, she does so with a keener eye than most: She knows the historic locale where it is filmed, Highclere Castle, inside and out – and relishes spotting things that may be amiss.

Although there is a historical advisor on the show, “she loves to pick out the mistakes,” Brian Hoey, author of At Home With The Queen, tells PEOPLE in this week’s issue. “They do tend to get it right. However, the Queen did notice on one episode that there was a young so-called British officer wearing medals which had not been awarded when he was supposed to be alive. He was fighting in the First World War and the medals on his chest did not come in until the Second World War.”

To celebrate the Queen’s milestone as the longest-reigning monarch in British history on September 9, we’ve gathered six other surprising insights into Her Majesty.

She does impressions.

Her cousin Margaret Rhodes tells PEOPLE, “She is quite deadpan and yet has a wonderful rollicking sense of humor.” Said to be a superb mimic (ask for her American accent!), she can do aircraft, too. “When Concorde used to fly over Windsor Castle, she developed an ability to mimic Concorde,” says Sally Bedell Smith, author of Elizabeth the Queen: The Life of a Modern Monarch.

Her musical taste isn’t highbrow.

The grand art of opera doesn’t excite her. And she is “lukewarm” about ballet, says Hoey. Musical theater is far more to her liking. “But it has to be the older musical theater by Rodgers and Hammerstein, like Carousel, Oklahoma or South Pacific. And she’s a huge fan of the big band sound.

She’s a star-gazer.

“She is really interested in space travel,” reveals Ingrid Seward, author of the new book, The Queen’s Speech. “She’s really knowledgeable about the stars and astronomy” – and she loves meeting astronauts.

She uses a special gadget to store her signature Launer handbags.

“For a while, she carried a bag hook around with her with a suction cup on it,” says Bedell Smith. “Someone I know watched her take it out of her handbag, apply a bit of spittle on it and put it on the under side of the table.” She also reveals that a soccer coach once had a peep inside her bag and said it had mundane “very practical and down to earth things items,” including “sweeteners, reading glasses, a comb, some tissues.”

Queen Elizabeth’s Changing Looks

She never wears a helmet on horseback.

The Queen, who turns 90 in April, is “very, very careful about not falling. If there is a circumstance where she thinks she’s in danger of tripping she takes extra care,” says Bedell Smith. Even now, she is still riding most days – and vigorously at that. “She is so comfortable on horseback and never worn a hard hat – she always wears a headscarf,” Bedell Smith notes.

She loves the dessert trolley.

Like her grandson Prince William, who chose a chocolate biscuit cake for his wedding day, she has a penchant for pudding. “She loves chocolate and sweet things,” Seward tells PEOPLE. “She has got a sweet tooth and has to curb it.”

For many more fascinating details and photographs of record-breaking Queen Elizabeth, pick up the latest issue of PEOPLE, on newsstands Friday

Want to keep up with the latest royals coverage? Click here to subscribe to the Royals Newsletter.