Bride-to-be Meghan Markle is to join Prince Harry as the couple begin their work with the Commonwealth Youth Forum together.
Just over a month ahead of the royal wedding, American star Ms Markle is attending an event in London on Wednesday as part of the high-profile Commonwealth Heads of Government Meeting (Chogm) week.
Harry has said the former Suits actress is "hugely excited" to be joining him in his Commonwealth duties.
The prince has been given a new role as Commonwealth Youth Ambassador by the Queen and opened the Youth Forum on Monday.
The pair, who will marry in Windsor on May 19, plan to support the Queen - the head of the Commonwealth - by taking a lead in Commonwealth youth matters.
It is unusual for someone who has not yet married into the royal family to be involved in a high-profile occasion such as the Chogm summit.
Ms Markle has given up her acting career to devote herself to being a full-time royal.
She has already spent Christmas with the royals at Sandringham- a break with tradition because she and Harry were not yet wed - and joined Harry on wide-ranging official engagements around the country.
At a reception at the Queen Elizabeth II Conference Centre in central London, Ms Markle and Harry will meet delegates who have been taking part in the Youth Forum's sessions.
The Forum is encouraging young people to debate challenges facing their generation, and agree youth-led initiatives to influence decision-makers.
Ms Markle and Harry will also attend a Women's Empowerment reception on Thursday, hosted by Foreign Secretary Boris Johnson, involving charities and organisations that work to promote global gender equality through girls' education.
The Chogm summit is staged every two years to discuss the major challenges facing the Commonwealth's 2.4 billion citizens.
Heads of the 53 Commonwealth nations are meeting in London and Windsor.