Prince Edward, Earl of Wessex and Sophie, Countess of Wessex attended a church service to mark The Queen's Platinum Jubilee at Holy Trinity Anglican Church.
Prince Edward and Sophie arrived in St Lucia on Saturday as they began their seven-day tour of the Caribbean.
The Earl and Countess of Wessex landed on the island after the Antigua and Barbuda Reparations Support Commission told them to avoid "phoney sanctimony" over slavery.