Prince Harry says he and US actress girlfriend Meghan Markle fell in love "so incredibly quickly" and it seemed proof that the "stars were aligned".
The fifth in line to the throne was speaking after the couple announced their engagement and plans to marry in spring 2018.
The couple told the BBC's Mishal Husain they met on a blind date and neither had known much about each other.
Prince Harry said "beautiful" Ms Markle "just tripped and fell into my life".
He believed Ms Markle and his late mother, Diana, Princess of Wales, would have been "thick as thieves... best friends".
Amazing surprise'
Prince Harry revealed he proposed earlier this month during a "standard, typical night for us" at his home in Kensington Palace as the couple were making roast chicken.
"It was just an amazing surprise. It was so sweet, and natural and very romantic. He got on one knee," Ms Markle said.
Prince Harry said: "She didn't even let me finish. She said 'Can I say yes'.
"Then there were hugs and I had the ring in my finger.
"I said 'Can I give you the ring?'. She said: 'Oh, yes, the ring'. It was a really nice moment. Just the two of us."
Turning to Ms Markle, Prince Harry said: "And I think I managed to catch you by surprise as well."