Princess Anne greeted hundreds of Chelsea pensioners at the Royal Hospital Chelsea to celebrate Founder's Day, also known as Oak Apple Day. It commemorates King Charles II escaping from parliamentary forces after the Battle of Worcester in 1651 by hiding in an oak tree to avoid being captured. Chelsea pensioners wear oak leaves on the scarlet uniforms in recognition. A golden statue of Charles II is also decorated with oak leaves for the occasion.

Founder's Day is held at the Royal Hospital Chelsea each year, on a date close to 29 May – Charles II's birthday. Inspired by Les Invalides in Paris, Charles II founded the Royal Hospital in 1682 as a retreat for veterans, with the idea that they could use it as a hostel instead of being paid pensions. The building was designed Sir Christopher Wren, whose other works include St Paul's Cathedral, the National Maritime Museum and Hampton Court Palace.