The couple, who announced their engagement to the world on Monday, are visiting a Terrence Higgins Trust World Aids Day charity fair, where they will meet representatives from charities and meet people living with HIV and Aids. 

The cause was close to the heart of Prince Harry’s late mother Princess Diana, who was hailed for changing attitudes towards HIV and Aids. 

In April 1987 Princess Diana opened the UK’s first purpose built HIV/Aids unit at London Middlesex Hospital, where she was famously pictured shaking the hand of a man suffering with the illness. 

Jason Knauf, Harry’s communications secretary, said he was looking forward to introducing his bride-to-be to a community that has “become very special to him”. 

He said US actress Meghan Markle could not wait to meet the people she has heard so much about from Harry. 

She was beaming as she waved and spoke to some of the 1,000-strong crowd who had gathered to catch a glimpse of royalty's newest couple.

Wearing a navy coat by Mackage, Meghan appeared to coordinate her outfit with Harry, who opted for a coat in the same colour, and a cream scarf to match his fiancee's midi-length dress.

Mr Knauf said Meghan plans to starts royal life with a “clean slate” and will focus her attention on the UK and Commonwealth. 

He said: “This is the counter that’s going to be her home now and that means travelling around, getting to know the towns and cities and smaller communities.”

They are understood to have been keen to make the Worlds Aids Day charity fair the key moment for their first outing after Prince Harry previously attempted to help break the stigma by taking a HIV test in public.

Ian Green, CEO of the Terrence Higgins Trust, said Diana had changed the narrative for those with HIV, adding: “I can’t emphasise enough the impact that Prince Harry and now Meghan will have.” 

Later, the royal couple will visit Nottingham Academy where they will meet schoolchildren and watch a performance of “Hip Hopera”. 

Prince Harry, 33, has spent a lot of time in Nottingham since the first time he met a group of young people there back in 2013 to explore issues surrounding youth violence. 

A year later, the royal launched the Full Effect programme which aims to crack down on youth violence in the city. 

Meghan got her first taste of the spotlight as a member of the Royal Family this week when the pair announced they would be getting married at Windsor Castle in May.

Meghan is a UN women’s advocate and has worked for World Vision. 

She will also become the fourth patron of the Royal Foundation of the Duke and Duchess of Cambridge and Harry. 

The foundation is behind mental health charity Heads Together and Prince Harry’s Invictus Games.