Philip was photographed sitting at the wheel of a 4×4, chatting to the Queen through the vehicle’s open window.
The couple were at the Royal Windsor Horse Show.
The 96-year-old was admitted to King Edward VII Hospital in central London last month for a planned hip replacement.
At the time, it was said that hip replacement patients have to walk aided for the first four to six weeks after surgery, meaning the Duke could be using a walking stick at Prince Harry and Meghan Markle’s wedding on 19 May at Windsor.
Palace officials have previously said he will attend the wedding if he is well enough.
Prince Philip, a former naval officer, retired from public life in August, saying at the time that he was no longer able to “stand up much”.
He had carried out around 22,000 solo royal engagements since Elizabeth was crowned Queen in 1953.
Meanwhile, The Royal Borough of Windsor and Maidenhead has reminded those hoping to catch a glimpse of the royal couple to arrive prepared for a long day.
Visitors will be able to watch the newlyweds’ carriage procession from Castle Hill, High Street, Sheet Street, Kings Road, Albert Road or the Long Walk, it said.
“They should ensure they have enough food, water, sun cream, waterproof clothing and essentials to cope with standing in crowds for several hours.
“Thousands of people are expected to crowd the streets.
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“It is crucial people have enough supplies and keep safe during the ceremony.”
:: Sky News will broadcast live in Windsor the week before the royal wedding with all the build up to the big day, with exclusive live coverage of the wedding in UHD in a special programme from 9am to 3pm on Sky News and Sky One on Saturday 19 May.