The Duke of Cambridge came to the aid of the Queen's representative in Essex when he took a tumble during a royal visit.
William and others rushed to help Jonathan Douglas-Hughes, vice lord-lieutenant of Essex, when he appeared to slip on wet pavement.
The Duke and Duchess had just arrived at Stewards Academy in Harlow for a visit when the mishap happened.
Mr Douglas-Hughes, who was wearing his ceremonial uniform complete with sword, fell backwards as the Duke was introduced to local dignitaries.
A gasp went up from around 30 well-wishers as he landed on his back and he was helped to his feet by William and others.
Mr Douglas-Hughes turned to William and said "Sorry about that", and the Duke replied "No, it's all right".