A closeup image of the Queen walking into the hospital to visit her husband today appears to show an envelope addressed to "HRH The Duke of Edinburgh".
Prince Philip turned 92 today, four days after undergoing exploratory surgery on his abdomen.
The Queen visited Prince Philip in hospital as the Palace described him as "comfortable and in good spirits" following an operation.
The Duke of Edinburgh will celebrate his 92nd birthday, as he did Christmas in 2011, in hospital.
Buckingham Palace say they expect him to remain there for up to a fortnight, but did not say what the exploratory operation was for.