The Duke and Duchess of Cambridge, Prince Harry and Meghan Markle will carry out their first joint engagement together.
The couples will take part in the first annual Royal Foundation Forum later on Wednesday where they will set out their future plans.
William, Kate, Harry and former Suits star Meghan will appear on stage together to discuss why The Royal Foundation was set up, the projects they are currently working on, and their ambitions for the years ahead.
American bride-to-be Ms Markle will formally become the fourth patron of The Royal Foundation following her high-profile wedding to Harry on May 19.
Under the theme Making A Difference Together, the event in central London will showcase programmes run or initiated by the Royal Foundation such as Heads Together, the Invictus Games, and United For Wildlife.
Launched in 2011, the foundation was set up by William and Harry as the main vehicle to pursue their charitable and philanthropic interests.
The Forum will be hosted by BBC presenter and Radio 1 newsreader Tina Daheley and the audience made up of invited guests, supporters of The Royal Foundation, programme partners and beneficiaries.
William is expected to be Harry's best man at his Windsor wedding and royal watchers will be keen to see the interaction between Kate and Meghan at their first appearance on official duties together.
The duke and prince's mother Diana, Princess of Wales forged a strong bond with her sister-in-law Sarah, Duchess of York in the early years.
But the pair fell out later on.
William and Kate expressed their delight at the news of Harry's engagement last year.
"We are very excited for Harry and Meghan. It has been wonderful getting to know Meghan and to see how happy she and Harry are together," they said.