Prince Charles appeared to make an emotional exit from his father's bedside on Saturday after he was the first royal to visit Prince Philip in hospital.
Charles was pictured in the front seat of his departing car, still wearing his face mask as he gazed out of the window.
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The royal arrived at King Edward VII’s hospital in London at around 3.20 pm on Saturday afternoon and stayed for around 30 minutes before making his exit shortly before 4 pm.
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It is understood the prince travelled from his home in Highgrove, Gloucestershire, to the hospital in central London, a journey of around 100 miles. He has since returned home.
It was revealed on Thursday that Philip is expected to remain in hospital into next week "for observation".
A royal source said: "Following consultation with his doctor the Duke of Edinburgh is likely to remain in hospital for observation and rest over the weekend and into next week.
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Prince Charles appeared emotional following a visit to his father in the hospital
"As we have said previously the doctor is acting with an abundance of caution. The Duke remains in good spirits."
In a statement released on Wednesday, Buckingham Palace said: "The Duke’s admission is a precautionary measure, on the advice of His Royal Highness’s Doctor, after feeling unwell. The Duke is expected to remain in hospital for a few days of observation and rest."
Charles stayed with Prince Philip for around 30 minutes
HELLO! understands that Prince Philip, who is said to be in "good spirits", walked into hospital by himself after travelling by car and that it was not an emergency admission. The stay in hospital is purely precautionary and the illness is not COVID-19 related.
The Queen has remained at Windsor Castle where she and her husband have been spending lockdown. On Thursday, she carried out her first official in-person event of the year, making one of her most senior royal aides, Vice-Admiral Sir Tony Johnstone-Burt, a Knight Commander of the Royal Victorian Order (RVO).
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