Kate Middleton's right-hand woman is stepping down after 10 years' service to the Royal Family.
Rebecca Deacon became the Duchess of Cambridge's private secretary shortly after the royal wedding in 2011.
The news was confirmed in a statement from Kensington Palace: "After a decade of service to the Duke and Duchess of Cambridge and Prince Harry, Rebecca Deacon will be stepping down as private secretary to the Duchess of Cambridge. She plans to leave the household in the summer.
"Their Royal Highnesses are incredibly grateful for all the hard work and support Rebecca has provided over the past ten years, and wish her well in the next phase of her career."
The news comes after reports of Ms Deacon's engagement and her plans to marry later this month.
Ms Deacon played an important role in the royal wedding and was often seen close by the duchess at public engagements.
A private secretary's duties include organising official programmes and engagements and ensuring Kate is briefed on who she is going to meet.