Prince Harry said today he is 'thrilled' to be marrying Meghan Markle and admitted he knew the Suits star was 'the one' from 'the first day we met'.
Meghan, 36, also showed the world her engagement ring designed by Harry himself containing two diamonds from Princess Diana's own personal collection set in a gold band.
Harry looked nervous but happy as they made their first public appearance since the announcement in the Sunken Garden at Kensington Palace, much loved by his late mother Princess Diana.
His fiancee stroked his arm lovingly as they spoke to reporters, who asked him: 'When did you know she was the one?' and he replied: 'From the very first time we met'.
He refused to say how he proposed saying: 'That will come later' but when asked if it was romantic he said: 'Of course it was' - but the couple didn't kiss for the cameras.
The prince said he was 'thrilled, over the moon' adding: 'Very glad it's not raining as well.' Meghan said she was 'so happy, thank you' before they wandered back into Kensington Palace beaming.
The happy couple made their first appearance in public since the announcement of their impending nuptials, posing for photographs in the Sunken Garden at around 2pm.
Harry and his brother William had white roses planted there in her memory when the 20th anniversary of her death fell in August.
Kensington Palace said the prince designed Ms Markle's engagement ring himself - using two stones which belong to his late mother.
The two outside stones are diamonds from the personal collection of Diana, Princess of Wales.
At the centre is a diamond from Botswana, a country that holds special significance for Harry who has visited many times since he was a child and they went on safari in September.
It is also a place the couple has spent time together over the last year and a half, Kensington Palace said.
The band is made of gold and the ring was made by Cleave and Company, Court Jewellers and Medallists to Her Majesty The Queen.
Harry, 33, who revealed a year ago he had fallen for the actress after a four to six month secret relationship, proposed to Meghan, 36, in London earlier this month.
Royal protocol dictated that fifth in line to the throne Harry had to ask his grandmother the Queen for permission to marry and she agreed in the month where she celebrated her own 70th wedding anniversary.
In a statement Her Majesty and Prince Philip said they are 'delighted for the couple and wish them every happiness' and this morning huge crowds of tourists and royal fans gathered outside Buckingham Palace.
Harry and his American fiancee, who divorced her first husband in 2013, will move into Nottingham Cottage in the grounds of Kensington Palace next door to his brother William and sister-in-law Kate.
The Duke and Duchess of Cambridge said in a joint statement: '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'. The boys' father Prince Charles said he was 'thrilled' and 'very happy indeed' for them.
Harry also asked Meghan's parents Thomas Markle and Doria Ragland, who divorced when their daughter was six, for her hand in marriage before popping the question a few weeks ago, it emerged today.
They said: 'Our daughter has always been a kind and loving person. To see her union with Harry, who shares the same qualities, is a source of great joy for us as parents'.
Harry and Meghan have not said where they will marry but most senior royals marry at Westminster Abbey, St Paul's Cathedral or the chapel at Windsor Castle. Sources have said it is likely to be a church wedding, especially after the Archbishop of Canterbury gave his blessing today.
But they are likely to wait until Prince William and Kate have their third child, which is due in April.
Bookmakers refused to take any more bets on the couple getting engaged last week as Meghan landed in London and started moving her belongings and two dogs to the UK.
Social media went into meltdown but they have had to wait until today to hear that the fifth-in-line to the throne has proposed to his actress girlfriend.
The couple will also took part in a broadcast interview that was aired last evening.
A Kensington Palace spokesman tweeted today: 'The Prince of Wales has announced the engagement of Prince Harry and Ms Meghan Markle.
'Prince Harry and Ms Markle became engaged in London earlier this month. Prince Harry has informed The Queen and other close members of The Royal Family.
'Prince Harry has also sought and received the blessing of Ms Markle's parents. The couple will live in Nottingham Cottage at Kensington Palace.
'The wedding will take place in spring 2018. Further details will be announced in due course.'
They have chosen to state they are getting married just before they spend their first proper Christmas together and will probably head to Sandringham to spend it with the Queen and the royal family.
Miss Markle's parents Thomas Markle and Doria Ragland said: 'We are incredibly happy for Meghan and Harry.
'Our daughter has always been a kind and loving person. To see her union with Harry, who shares the same qualities, is a source of great joy for us as parents.
'We wish them a lifetime of happiness and are very excited for their future together.'
Prime Minister Theresa May said: 'I would like to offer my very warmest congratulations to HRH Prince Harry and Meghan Markle upon their engagement.
'This is a time of huge celebration for two people in love. On behalf of myself, the Government and the country, I wish them great happiness for the future.'
Her predecessor David Cameron said: 'Congratulations to Prince Harry and Meghan Markle. Wonderful news and I wish them a long and happy life together.'
Foreign Secretary Boris Johnson said: 'Huge congratulations to Prince Harry and Meghan Markle - fantastic news! Here's to a happy and long life together.'
Archbishop of Canterbury Justin Welby added: 'I am absolutely delighted to hear the news that Prince Harry and Meghan Markle are now engaged.
'I have met Prince Harry on a number of occasions and have always been struck by his commitment and passion for his charities, and his immense love for his family.
'Marriage is a special and joyous commitment, one that Jesus celebrated together with friends at the wedding in Cana.
'I am so happy that Prince Harry and Ms Markle have chosen to make their vows before God.
'I wish them many years of love, happiness and fulfilment and ask that God blesses them throughout their married life together.
© Associated Newspapers Ltd.