updated 01/20/2012 AT 9:00 AM ET
•originally published 01/20/2012 AT 10:45 AM ET
Rainy and 48 degrees in London on Friday. No matter: The Duchess of Cambridge – with parents Michael and Carole, and sister Pippa – is off on a sunny vacation, PEOPLE has confirmed.
Passengers on a British Airways flight from London’s Gatwick Airport to St. Lucia in the Caribbean were surprised to see the family in the first class section on Wednesday, a photographer blogged. Their presumed final destination: one of their regular holiday haunts, the private isle of Mustique.
It is believed that Prince William is not with them, as the search and rescue helicopter pilot is spending this week at his RAF base in Anglesey, Wales, after hunting last weekend on an estate in Spain with brother Prince Harry.