Harry and Meghan flew to New York City to attend the United Nations' informal meeting held by the General Assembly to mark the special day.
WATCH: Prince Harry shares emotional speech at UN meeting
At the event, which saw the Deputy Secretary-General and the President of the General Assembly give remarks, Harry took centre stage as he gave the keynote address, with Meghan proudly watching from the audience.
Harry and Meghan arrived hand-in-hand at the UN General Assembly
Harry spoke about climate change and poverty, making references to Nelson Mandela's life and legacy and what has been learnt from the late president's struggle.
Challenges that the anti-apartheid activist faced in his lifetime, which are still ongoing today, include the divide between rich and poor, racial intolerance, and hunger and food insecurity.
The Duchess looked chic in a black pencil dress
He spoke about his love for Africa, a continent he first visited when he was 13 years old and where he went to seek refuge after the death of his mother Diana, Princess of Wales.
It was then that Harry sweetly called Meghan, who he whisked to Botswana on their third date, his "soulmate".
"Since I first visited Africa at 13 years old, I've always found hope on the continent. In fact, for most of my life, it has been my lifeline, a place where I have found peace and healing time and time again," he said. "It's where I've felt closest to my mother and sought solace after she died, and where I knew I had found a soulmate in my wife. And it's why so much of my work is based there."
The Duke called Meghan his "soulmate" during his speech
The Duke also spoke about looking back on a photograph of his mum Diana with Nelson Mandela as a source of comfort.
"On my wall, and in my heart every day, is an image of my mother and Mandela meeting in Cape Town in 1997," said Harry. "The photo was presented to me by the late Archbishop Desmond Tutu, whose friendship and inspiration were their own treasured gift. My wife and I had the honour of introducing our four-month-old son to him back in 2019.
"When I first looked at the photo, straight away what jumped out was the joy on my mother's face. The playfulness, cheekiness, even. Pure delight to be in communion with another soul so committed to serving humanity."
During the two-hour meeting, the 2020 UN Nelson Mandela Prize was also awarded to Mrs. Marianna V. Vardinoyannis of Greece and Dr. Morissanda Kouyaté of Guinea. The prize, which is given every five years, recognises people who have dedicated their lives to the service of humanity.
Harry gave the keynote speech at the General Assembly's informal meeting
Harry and Meghan appeared in high spirits as they arrived at the UN General Assembly on Monday morning.
The father-of-two looked smart in a navy suit and tie, while former Suits actress Meghan was typically stylish in a black pencil dress. She had her hair swept up into a tight ponytail and accessorised with a black Mulberry bag.
The Duke made references to Nelson Mandela's life and legacy
The Sussexes travelled to the East Coast from their home in California. It's not known if they were accompanied by their two children, son Archie, three, and one-year-old daughter Lilibet.
Harry, 37, and Meghan, 40, previously attended the UN General Assembly in September 2021 but they did not take part in the speeches.
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