Princess Anne's retirement plans revealed amid frustration with Prince William

Princess Anne, the younger sister of King Charles, is expected to continue to support her brother for 15 more years.

This has been disclosed by the royal insiders as Princess Anne is set to celebrate her 75th birthday.

The Times, citing the royal sources, has reported that the Princess Royal will follow in her father Prince Philip’s footsteps as she is thought to be planning a gradual reduction in her workload at 80 before finally fully retiring a decade later.

The source tells the publication "She has said her plan is to push on (with work) until she is 80, then start winding down a bit, and then copy the (late) Duke of Edinburgh and wind down completely at 90."

The insider said: "The head of state has to go on but the princess is in a position where she can wind down and say, 'I've done my bit', just like the Duke of Edinburgh did."

Princess Anne maintains strong relationship with King Charles, however, the insider close to her has noted her frustration with Prince William's workload, particularly regarding investitures at Windsor Castle.

The insiders have claimed that the Princess Royal is ‘annoyed’ with Prince William.