Princess Diana reportedly made one crucial mistake when she refused to participate in the royal family’s weekly barbecue sessions.

In the book “The Queen and Di: The Untold Story,” royal author Ingrid Seward revealed that after Prince Charles and Princess Diana’s honeymoon, the latter had a hard time adapting with her husband’s family’s rituals.

“Within a week of her return as Princess of Wales, she was sulkily refusing to go. She just about managed to drag herself out for the occasional picnic, but she would try everything to get out of barbecues… This was considered ‘extremely bad form,’” she said.

And since the weekly barbecues were a perfect time for the royal staff to get time off from their work, Princess Diana’s refusal to attend didn’t sit well with the aides. In the book “Charles: The Untold Story,” royal author Ross Benson said that the Princess of Wales wasn’t very popular with the royal staff.

“It was, everyone agreed, bad form on Diana’s part and the Queen was not amused,” he said. But to everyone’s surprise, one member of the royal family stuck up for the mom of two.

Princess Margaret defended Princess Diana by telling her older sister, Queen Elizabeth II, to allow the newest member of the royal family to do whatever she wants to do. After this confrontation, Her Majesty laid the issue to rest.

Meanwhile, Seward also said that Princess Diana didn’t just dislike the barbecues and picnics of the royal family. She also didn’t like to talk to strangers while she’s out in public.

“No matter how hard she tried, Diana never succeeded in getting rid of that implosive feeling of claustrophobia which pressed on her whenever she was called upon by the crowds. Almost at the end of her life, she told: ‘I still feel really insecure about going out and meeting people I don’t know… After all these years, I never really got over it,’” she said.

Princess Diana
Britain’s Princess Diana arrives on Oct. 4, 1990 for a charity gala at the Departmental Auditorium in Washington. Kevin Larkin/AFP/Getty Images