The Queen was forced to pull out of an investiture ceremony this morning after suffering "mild discomfort" with her ankle, a palace spokesperson said.
Prince William took the Queen's place in the ceremony - the second time he has performed an investiture.
The Queen's condition is not a result of an injury, the palace said. She is expected to fulfill her engagements tomorrow.
"The Queen has a very busy schedule for the rest of the week, including a trip to Manchester with the Duke of Duke of Edinburgh on Thursday," a palace spokesperson added.