London - It was love at first sight for Prince Harry and Meghan Markle, who both quickly sensed their brief encounter on a blind date could blossom into something much, much bigger.

They were set up by a mutual friend when US actress Markle was passing through London in July 2016, with the couple later revealing they knew little about each other. The speed of their relationship surprised them both.

"The fact that I fell in love with Meghan so incredibly quickly was a confirmation to me that all the stars were aligned. Everything was just perfect," said Harry.

Less than two years later, they will tie the knot at Windsor Castle on May 19, sealing a relationship that rapidly grew outside of the media spotlight - and survived when it went public in explosive fashion.

When the couple first met for a drink, both were taken aback.

She was 34 and a divorcee of three years; he 31 and with a few foundered relationships and his 10-year army career recently behind him.

Harry had never heard of Markle or watched "Suits", the US television legal drama series she had starred in since 2011.

"I was beautifully surprised when I walked into that room and saw her," he recalled, and thought to himself: "I'm going to really have to up my game here!" .

Bonding in Botswana

Bonding over their passion for the good causes they represented, they immediately set up a second date - for the following day.

A few weeks later, he persuaded her to join him camping out for five days in Botswana, which Harry called a "huge leap" to take so soon - but one that paid off.

"We were really by ourselves, which was crucial to me to make sure that we had a chance to get to know each other," he said.

As Markle continued filming "Suits" in Toronto, the pair never went longer than two weeks apart.

Their romance was undercover for the first five or six months, and largely conducted through nights in behind closed doors.

"We were able to really have so much time just to connect," said Markle.

The prince said the royal family had been very supportive of the relationship, including his grandparents Queen Elizabeth II and Prince Philip, his father Prince Charles, as well as his brother Prince William and his wife Kate.

Harry said they had frank conversations about what her future could entail and found it a "huge relief" to have finally found someone comfortable with the pressure and lifelong job that he comes attached with.

Royal author Andrew Morton, who penned a biography of Markle, said the speed with which she fell for Harry was surprising as the TV star was a lifelong cautious character.

"He was more of the supplicant than Meghan. He had more to gain and Meghan has more to lose by her agreeing to be his bride," Morton told AFP, in an unusual role reversal for the prince.

'This is not a game'

Harry publicly confirmed they were dating in November 2016 with a highly unusual statement blasting racist "abuse and harassment" directed towards her.

"It is not right that a few months into a relationship with him that Ms Markle should be subjected to such a storm," his communications secretary Jason Knauf said.

"This is not a game - it is her life and his." The angry statement, going way beyond the lengths Harry went to for previous girlfriends, confirmed how seriously he was treating this relationship.

Eventually, Harry proposed in November 2017.

The couple were having a cosy night in at Nottingham Cottage, the two-bedroom home they now share in the grounds of London's Kensington Palace, roasting a chicken.

"It was just an amazing surprise. It was so sweet and natural and very romantic. He got on one knee," the actress said.

Markle said yes before Harry had finished proposing or even produced the ring.

They announced their engagement on November 27 last year and she was swiftly integrated into the royal fold, making her first official public appearance with Harry on December 1 and spending Christmas with the family.

The pair will throw themselves into causes they wish to champion, while Harry has suggested that their joint focus will be on the Commonwealth, particularly youth.

"Both of us have passions for wanting to make change for good," he said.