The 94-year-old monarch wrote to them of the decision and also said that all their honorary military appointments and royal patronages will be redistributed among other working members of the royal family.
While his official diary of engagements come to an end on Wednesday, the Palace has said the Duke may still decide to attend some events alongside the Queen.
"The Sussexes will not use their HRH titles as they are no longer working members of the Royal Family. The Duke and Duchess of Sussex have shared their wish to repay Sovereign Grant expenditure for the refurbishment of Frogmore Cottage (believed to be 2.4 million), which will remain their United Kingdom family home," a statement from the Buckingham Palace read.