Professor Sir Huw Thomas is Head of the Medical Household and Physician to the Queen, a role he has held since 2014.
WATCH: The Queen tests positive for COVID-19
He was knighted last year after being invested with the Insignia of a Knight Commander of the Royal Victorian Order.
It is likely the Queen wanted to thank Prof Sir Huw personally for his care of her and the royal family.
Prof Sir Huw, who is also a professor of gastrointestinal genetics at Imperial College London's department of surgery and cancer, has previously spoken of how grateful he was to be recognised for his service.
The Queen held an in-person audience at Windsor Castle on 16 February
Speaking at Imperial at the time of his knighthood, he said: "It's been a busy couple of years in this role, so I feel very grateful to have been recognised for my service to date."
He added: "You very much become part of that organisation and become the personal doctor to the principal people in it, who are patients just like other patients.
"With the pandemic, the key priority of the Medical Household is trying to make sure that the people under its care are kept safe."
The Queen has also been spotted using a walking stick of late
Concerns about the Queen's health were first raised back in October 2021 when she had her first hospital stay in eight years.
It is likely to have been Prof Sir Huw who advised the head of state to take things easy after she underwent preliminary tests in King Edward VII's Hospital on 20 October 2021.
A sprained back also prevented her from attending the Remembrance Sunday service in London in November, and she was forced to pull out at the last minute.
The Queen recently marked the start of her Platinum Jubilee year
Following the Queen's coronavirus diagnosis, Buckingham Palace has said the monarch is experiencing mild cold-like symptoms but expects to continue light duties at Windsor Castle over the coming week.
Professor Sir Huw has also been involved in delivering some of the younger members of the Royal Family.
He was part of the team who looked after the Duchess of Cambridge when she gave birth to daughter Princess Charlotte in 2015 and youngest son Prince Louis in 2018 at St Mary's Hospital, Paddington, alongside Guy Thorpe-Beeston, surgeon gynaecologist to the royal household, and consultant gynaecologist Alan Farthing, surgeon gynaecologist to the Queen.
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