The Duchess of Sussex beamed at an exhibition charting the life, career and politics of one of her heroes - Nelson Mandela.
She was joined by her husband the Duke, whose family had a close relationship with the former statesman, who campaigned throughout his life to end South Africa's apartheid regime.
Mandela and the Queen built up a firm friendship, with South Africa's former president calling her "Lizzie" according to his daughter Zindzi Mandela.
Harry has visited a number of sites associated with Mandela, from his prison cell on Robben Island in 2008, where he was imprisoned for 18 years, to a tour of the statesman's offices, where he met his widow Graca Machel, in 2015.
Around 300 people were invited inside on Friday, including Mandela's goddaughter Tanya von Ahlefeldt, who managed to capture a stunning photograph of the royal couple in front of December 6 2013 The Daily Telegraph front page, the day after the great man died.
She told The Telegraph the Duke and Duchess were "beautifully elegant" and that the event was "fabulous" and a "great tribute".
Leading former anti-apartheid campaigner Lord Hain, who is chairman of the Nelson Mandela Centenary Exhibition, said: "London was the centre of the anti-apartheid struggle.
"It was here that Mandela's close comrade Oliver Tambo lived, led and directed the worldwide struggle, from military operations in southern Africa to diplomatic lobbying of the United Nations.
"We thought to commemorate Mandela's centenary there should be an exhibition in London.
"It was curated by the Apartheid Museum in Johannesburg and I asked their royal highnesses to come as he does charitable work in southern Africa and she has said before that Nelson Mandela is one of her heroes.
"So we thought it would be very, very fitting for them to be at the launch and we're thrilled they accepted."
Among the guests was a former prison inmate of Mandela, and his granddaughter Zamaswazi Dlamini-Mandela.
The exhibition, at the Southbank Centre's Queen Elizabeth Hall, traces Mandela's career from activist to president through six themes: character, comrade, leader, prisoner, negotiator and statesman.
It is the first time the exhibition will be shown in the UK after successful runs in various forms around the world, including six weeks at the Paris Town Hall in 2013.
Harry and Meghan arrived in brilliant summer sunshine, with the duchess wearing an outfit by House of Nonie.
Prince Harry visited Mr Mandela's cell, where he spent 18 years imprisoned by the apartheid regime, during a trip to South Africa's Robben Island in 2015.
He also toured the statesman's offices and met his widow Graca Machel in 2015.
During their visit to the South Bank, the Duke and Duchess toured the exhibition and at each themed panel will meet people associated with the displays and Mr Mandela's work.
The guests include Thembi Tambo, South Africa's High Commissioner to the UK and daughter of anti-apartheid politician Oliver Tambo, who was a close colleague of Mr Mandela.
Items on display include a Collected Works of Shakespeare, which was smuggled onto Robben Island and features annotations made by Mr Mandela and his contemporaries.
There is also a letter of thanks from the statesman to the British public written on April 16, 1990, the day Mr Mandela attended the Wembley concert held in his honour, he thanks the British public for their "overwhelming generosity".
The Southbank Centre has closed one of its most popular attractions of the summer in preparation for the royal visit.
Offering relief to those struggling with the unprecedented heatwave, the outdoor fountains near the Thames have have become a magnet for families with children running in and out of the water to cool off.
Visitors please note, for security purposes relating to the royal visit of the Duke and Duchess of Sussex, our Appearing Rooms fountain will only be open to the public from 4pm today. Thank you for your understanding. pic.twitter.com/fm434spBYn
— Southbank Centre (@southbankcentre) July 17, 2018
But they will be out of action to the public in the capital today until 4pm.