Why Queen Elizabeth Missed Several Platinum Jubilee Events

Queen Elizabeth II missed several of the Platinum Jubilee events celebrating her 70 years on the British throne last week because of her mobility issues. One royal observer said the 96-year-old monarch would "not want to stumble" in front of the cameras. The queen only appeared at a handful of Jubilee events between Thursday and Sunday.

Queen Elizabeth joined Prince Charles, Prince William, and other senior members of the royal family for the Trooping the Colour ceremony at the Buckingham Palace balcony on Thursday. Later that same day, she lit the Platinum Jubilee beacons. However, she missed the service of thanksgiving in her honor on Friday. She did not attend any public events until Sunday when she made a surprise appearance on the palace balcony to mark the end of the celebrations.

Buckingham Palace said the Queen experienced "some discomfort" after attending the Thursday events. Royal historian Robert Lacey told PEOPLE the Queen has "high expectations" for herself, which may have led to her decision to skip some Jubilee events. "She would not want to stumble – not for her own sake but for the distress, it would cause other people," Lacey said.

Another source told PEOPLE Queen Elizabeth's mobility issues "flared up" on Thursday. She was seen using a cane on the palace balcony. On Friday, Kate Middleton reportedly told an attendee at a reception that the Queen was "fine," but the Trooping the Colour ceremony was "very tiring" for her. The monarch "had a lovely, lovely time," the Duchess of Cambridge said, reports the Press Association.

Queen Elizabeth's health has come under scrutiny since last fall when she was previously hospitalized. In recent months, her mobility issues have become more public, and she is unable to stand for long periods. She has been seen using a cane during her recent public events. Although she attended the Trooping the Colour, she did not join her family in the main parade for the first time.

The Queen referenced missing Jubilee events in a statement she released late Sunday to thank the U.K. public for their support. "While I may not have attended every event in person, my heart has been with you all; and I remain committed to serving you to the best of my ability, supported by my family," Queen Elizabeth said. "I have been inspired by the kindness, joy and kinship that has been so evident in recent days, and I hope this renewed sense of togetherness will be felt for many years to come. I thank you most sincerely for your good wishes and for the part you have all played in these happy celebrations."