Police have blocked off the road outside the hospital where Prince Philip is being treated for an infection.
A screen was erected around a waiting car, with the back doors open, suggesting the prince or other dignitary might be leaving King Edward VII's Hospital in London.
The 99-year-old later left the hospital after a month long stay - his longest ever.
The Queen's husband was initially taken to King Edward VII's on February 16 as a precaution after feeling unwell and was later revealed to be battling an infection.
He was later transferred to NHS-run St Bartholomew's Hospital in relation to an underlying heart condition - and then back to King Edward VII's where he recovered from an infection.
His month-long stay beats the Duke of Edinburgh previously longest hospital stint of 11 days in 2013 after he had an operation on his abdomen.
The pre-existing heart condition wasn't mentioned extensively before in reports on the duke's health although he has had procedures on his chest after suffering chest pains, such as in 2011.
The Queen had reportedly been unable to visit her husband of 73 years in hospital due to coronavirus restrictions.
But the royal couple's eldest son Prince Charles made a 30-minute visit on February 20, before he was initially transferred for the op.
Earlier this month the Philip moved hospital for the second time after heart surgery and at the time it was said he was expected to stay for several days.
He was transferred back to a private hospital after successfully undergoing a procedure to treat a heart condition.
Buckingham Palace said in a statement at the time: "Following The Duke of Edinburgh's successful procedure at St Bartholomew's Hospital on Wednesday, His Royal Highness has been transferred to King Edward VII's Hospital this morning.
"The Duke is expected to remain in hospital for continuing treatment for a number of days."
The duke had spent most of lockdown residing at Windsor Castle with the Queen for their safety, alongside a reduced household of staff dubbed HMS Bubble.
