Pop star Lily Allen shared her excitement on Twitter after she spotted Kate Middleton in Gloucestershire on Wednesday morning.
She tweeted: "Just saw the actual Duchess of Cambridge casually walking around Tetbury. Wowsers."
The Duke and Duchess of Cambridge were in the Gloucestershire town preparing for William's 30th birthday celebrations there this week.
The future King marked the milestone age in what was said to be a low-key and private fashion at St James's Palace yesterday.
Days before Lily spotted the couple, who have been married for just over a year, they were at the Beaufort Polo Club with their puppy Lupo.
The Duchess of Cambridge watched her husband play in a polo event to raise funds for charities Child Bereavement, the Tusk Trust and Well Child, while in a pair of casual skinny jeans.