Prince Harry declared he was "thrilled" and "over the moon" as he and his fiancee Meghan Markle appeared together in public for the first time after their engagement was announced.
And he admitted that he had known American actress Ms Markle was "the one" from the moment they met.
"When did I know she was the one? Very first time we met," the prince said.
Smiling and giggling throughout the brief photo opportunity in the Sunken Garden at Kensington Palace on Monday afternoon, the couple stood hand in hand and waved at well wishers.
Ms Markle said she was "so very happy" to be engaged to Harry.
But they did not reveal how Prince Harry proposed with Harry adding: "That will come later." The pair are giving a television interview to be broadcast on Monday evening.
Their long-anticipated engagement was announced by the Prince of Wales on Monday morning with a statement saying the couple, who have been dating for 16 months, will marry in the spring next year.
There are "no plans" for a bank holiday on the day of the wedding, Downing Street has said.
Prince Harry designed the engagement ring for Ms Markle himself using two diamonds from the personal collection of his late mother.
The gold ring, made by Cleave and Company, Court Jewellers and Medallists to Her Majesty The Queen, features two stones that belonged to Diana, Princess of Wales on the outside.
In the centre is a diamond from Botswana, a country that holds special significance for Prince Harry and where they had spent some time together as a couple.
Video report by ITV News correspondent Angus Walker
While a date has not yet been announced for the wedding, one is thought to have already been fixed, with Royal diaries synced to ensure that everyone can attend.
Ms Markle's parents Thomas Markle and Doria Ragland have said they are "incredibly happy" with the couple's engagement, adding: "We wish them a lifetime of happiness."
The Queen and Duke of Edinburgh have said they "are delighted for the couple and wish them every happiness".
On a visit to Dorset, the Prince of Wales said he was "thrilled" and "very happy indeed" for Prince Harry and Ms Markle.
While the Duke and Duchess of Cambridge said it had been "wonderful... to see how happy" Ms Markle and Prince Harry are together.
In a statement, the pair said: "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."
Prince Charles meanwhile said he was "thrilled" by the news.
The couple will take part in a broadcast interview this evening, a Kensington Palace spokesperson said.
The relationship so far
The fifth-in-line to the throne was first introduced to the American actress at a private members club in London in Summer 2016, with a friend of the pair who managed the Soho House chain making the introductions.
When the story of their romance hit the headlines a few months later, Prince Harry was alarmed at the way the press began looking into Meghan's family and past relationships and took the highly unusual step of issuing a strongly worded statement.
It read: "The past week has seen a line crossed. His girlfriend Meghan Markle has been subject to a wave of abuse and harassment."
It went on: "He knows commentators will say 'this is the price she has to pay' and that 'this is part of the game'. He strongly disagrees. This is not a game it is her life and his."
The statement was the first official confirmation the pair were in a relationship.
Days later the 36-year-old actress was seen in London, amid unconfirmed reports she was enjoying her first stay at Kensington Palace since the couple's relationship was made public.
In November 2016, on a trip to Antigua and Barbuda, the island's prime minister publicly invited the blushing 33-year-old to choose the island as his honeymoon destination.
On his way back from the Caribbean islands, Prince Harry flew to Toronto on a 1,700-mile detour to visit Ms Markle rather than flying straight back to London. The Royal's trip to Canada came under criticism as it contravened guidelines which discourage royal work trips - which are paid for by the taxpayer - from being combined with personal travel.
In March 2017 the pair were reported to be setting up home together in an apartment at Kensington Palace.
In September 2017, Ms Markle spoke openly about her relationship with the prince in an interview with Vanity Fair, in which she told the magazine: "We're two people who are really happy and in love. We were very quietly dating for about six months before it became news."
The high-profile interview led to speculation that an engagement between the pair was imminent.
Just weeks later the couple chose to be photographed together in public for the first time at the Invictus Games - the event for wounded military veterans which Harry founded in 2014.
This year's Invictus Games took place in Toronto - the city in which Meghan Markle lives while she films the latest series of the hit TV show, "Suits".
The prince and actress attended a wheelchair tennis session. They arrived holding hands and were seen chatting with younger members of the audience.
In October 2017, the pair met with the Queen for afternoon tea. The couple needed Elizabeth II's permission to marry.
Will Meghan become a princess when the pair marry?
Tradition dictates that royal men receive a title when they marry, with Prince Harry expected to be made the Duke of Sussex.
After saying her vows, Ms Markle would become both an HRH and a duchess - likely Her Royal Highness The Duchess of Sussex (if Harry becomes the Duke of Sussex).
Should Prince Harry turn down a title, then Ms Markle would be known as HRH Princess Henry of Wales, since she is not entitled to be known as Princess Meghan.
The world responds
Prime Minister Theresa May offered her "very warmest congratulations" to the newly-engaged couple.
While Scotland's First Minister, Nicola Sturgeon wished the pair "a lifetime of love and happiness together".
Former prime minister David Cameron also offered his well-wishes to the pair.
Even former US president Barack Obama reached out to offer congratulations.