Queen Elizabethis taking a break amid her four-day Platinum Jubilee celebration after a whirlwind day ofTrooping the Colour celebrationsleft her feeling “some discomfort,” the palace announced on Thursday.

The monarch said that she will not be attending the National Service of Thanksgiving in her honor at St. Paul’s Cathedral on Friday. She will, however, still participate in a beacon lighting ceremony on Thursday evening.

“The Queen greatly enjoyed today’s Birthday Parade and Flypast but did experience some discomfort,” a spokesperson for Buckingham Palace said.

“Taking into account the journey and activity required to participate in tomorrow’s National Service of Thanksgiving at St Paul’s Cathedral, Her Majesty with great reluctance has concluded that she will not attend,” the statement continued.

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“The Queen is looking forward to participating in tonight’s Beacon lighting event at Windsor Castle and would like to thank all those who made today such a memorable occasion.”

Anthony Harvey/Shutterstock

Camilla Duchess of Cornwall, Prince Charles, Queen Elizabeth II, Prince Louis, Catherine Duchess of Cambridge, Princess Charlotte, Prince George and Prince William Trooping The Colour - The Queen’s Birthday Parade

A source tells PEOPLE that the Queen’s episodic mobility issues flared during the course of the day on Thursday. She was pictured using her cane on the palace balcony as she took the salute and viewed the flypast alongside members of the royal family.

Queen Elizabeth.Tim Rooke/Shutterstock

The Queen, attends celebration marking her official birthday, during which she inspects troops from the Household Division as they march in Whitehall,

It’s a regrettable but sensible decision based on the physical demands of tomorrow’s service at St. Paul’s Cathedral, the source adds. It was always the Queen’s hope that she would attend rather than a firm commitment.

Queen Elizabeth and Prince Louis.Aaron Chown/PA Images via Getty Images

Queen Elizabeth II speaks to Prince Louis on the balcony of Buckingham Palace

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The Queen has been experiencing mobility issues in recent months and finds it difficult to stand for long periods. She has been using a walking cane and even complained about mobility problems, joking during an in-person meeting: “Well, as you can see, I can’t move!”

She also recently shared a small glimpse into herbattle with COVID-19earlier this year, revealing that “it does leave one feeling very tired and exhausted.”

source: people.com