Fans were quick to point out Harry's likeness to the Duke, with one writing: "I thought it was Harry."
Another said: "This is the first time I saw that Prince Harry looks exactly like his grandfather."
"For anyone saying Harry is not Charles's son, he looks exactly like Philip here!" one more added.
Harry touched down in London yesterday for the funeral, with his pregnant wife Meghan Markle staying home in the US.
It's his first return to Britain since quitting royal duties last year and last month's explosive Oprah interview.
According to royal expert Kate Nicholl, he is due to enter quarantine for five days before meeting up with his grandmother the Queen.
While the two have reportedly been in "regular contact", it is the first time Harry will have faced the monarch since his and Meghan's bombshell televised interview.
It is understood he will be staying at Frogmore House in Windsor, the couple's UK home in the grounds of Windsor Castle.
Prince Philip's funeral will be the first time Prince Harry has been seen in public with his family since the Commonwealth Day service in March 2020.
The funeral will be held on Saturday afternoon local time. Prince Philip's four children, Princes Charles, Prince Andrew, Prince Edward and Princess Anne, will join Princes Harry and William following the coffin on foot to St George's Chapel at Windsor Castle.
The route of the procession will be lined by representatives from the Royal Navy, the Royal Marines, the Highlanders, the 4th Battalion Royal Regiment of Scotland and the Royal Air Force, according to The Sun.
Guns will be fired by The King's Troop Royal Horse Artillery for each minute of the procession.
A Guard of Honour will receive the coffin as it arrives at the chapel.
The funeral service will begin with a nationwide minute's silence at 3pm.
