The Duke and Duchess of Sussex had to "find their own voice", just like Nelson Mandela, the former South African president's granddaughter has insisted.

Prince Harry and his wife Meghan have faced criticism for speaking out against the royal family since stepping down to start a new life in the US almost four years ago, but Ndileka Mandela has insisted it is important they are allowed “room to voice out whatever their misgivings are”about the institution.

The activist compared the couple's situation to that of the famed anti-apartheid campaigner, who fled to Johannesberg in 1941 to avoid an arranged marriage set up by his guardian.

Appearing on 'Sunday With Laura Kuenssberg', Ndileka was asked if she felt the couple had been victims of racism and said: “I believe that Harry and Meghan had to find their own voice, in a similar way that grandad had to find his own voice when he had to run away from an arranged marriage.

“So they should be given, like any other person, room to voice out whatever their misgivings are. I cannot speak to whether Harry and Meghan’s children have been discriminated. I don’t have first-hand information of that.

“However, I can say that he should be allowed to voice out whatever it is that he wants to voice out and to choose his own path. Had grandad not chosen his own path when he ran away from an arranged marriage, we would not have the South Africa that we talk about today.

“So people should be allowed to present different journeys and should be allowed to walk different journeys in life.”

Despite speaking up in support of Harry and Meghan - who have children Prince Archie, four, and Princess Lilibet, two, together - Ndelika previously hit out at the couple for using her grandfather's words in their Netflix documentary series ‘Live to Lead’.

But revealing how the move left her "deeply upset", Ndileka told The Australian: "Harry needs to be authentic and stick to his own story, what relevance does grandad’s life have with his?"

In the trailer for the documentary, which focuses on inspirational public figures such as Ruth Bader Ginsburg and Greta Thunberg, Harry is heard saying: “This was inspired by Nelson Mandela... who once said what counts in life is not the mere fact that we have lived.”

Meghan added: “It is what difference we have made to the lives of others that will determine the significance of the life we lead.”

Ndileka fears the couple are drawing a comparison between her grandfather’s release from prison and their decision to leave Britain when they stepped down as senior members of the royal family.

She added: “Their marriage can never be compared to the celebration of grandad’s release... that’s chalk and cheese, there is no comparison.

"I don’t believe he nor Meghan have ever properly met granddad, maybe when Harry was young at Buckingham Palace, but they are using his quotations in the documentary to draw in people and make millions without the Mandela family benefiting.

“I know the Nelson Mandela Foundation has supported the initiative but people have stolen grandfather’s quotes for years and have used his legacy because they know his name sells – Harry and Meghan are no different from them."