The Queen congratulated Prince Harry on his work for an African charity as she toured a garden inspired by the organisation at the Chelsea Flower Show.
It was a family affair at the world-renowned horticultural show as the Queen and Duke of Edinburgh were joined by the Prince of Wales and Prince Harry as they toured the displays.
Fresh from his tour in Australia and New Zealand, Harry was reunited with his father and grandmother at Chelsea, greeting each with a kiss on the cheek.
The family toured a garden created for Sentebale, a charity founded by the prince which helps vulnerable children in the small southern African country of Lesotho.
The Queen said well done to Harry, who took a keen interest in the garden's design.
Philip Green, chairman of Sentebale, said: "Harry is very authentic. If he says something, it's his judgment, it's not spin.
"He said it was perfect. I said, 'do you really mean it's perfect?'. He said 'Yes, I wouldn't change a thing'.
"It is an extreme privilege for us to have three generations of the royal family in one garden - for a high-profile but relatively small charity.
"The Queen walked the length of the garden. She was very complimentary about the planting."
Garden designer Matt Keightley, 30, said: "They genuinely seemed interested and fascinated in the details.
"It was amazing to have so many of the royals."
He said Harry had taken a keen interest in the project and explained the garden to his father and grandparents.
The garden is inspired by a children's centre the charity is building in Lesotho, and the prince hopes that touches from the garden can be added to the design of the centre.
Mr Keightley said: "Harry has been intrigued about the correlation between the Chelsea garden and the children's centre so he was explaining to them which details would be taken out to the children's centre.
"Before they arrived the prince was talking about the one Lesothian poppy which is flowering in the garden and joking about whether we should have offered it up for a button hole. I said there is only one so we couldn't possibly.
"The royal family members were interested in how many of the plants are native to Lesotho. I said 20%."
He said the Queen "really liked" the trail of footprints that weave their way through the garden, made from the footprint of a child in Lesotho.
The designer joked that he and Harry were worried they might be marked down by the judges because a television crew had been filming in the garden and left dirty footprints.
There was a dash to spruce up the garden before the judges arrived to inspect it.
He said: "I had scrubbed the paving down for about an hour and a half. I was trying to keep everyone off it and then out of the corner of my eye I looked up and saw people walking through.
"I screamed 'No!'. I looked up and it was the judges - so I had screamed at them which was unfortunate. I think they found it quite funny."
The Queen wore a sky blue coat by Karl Ludwig - which she last wore at Royal Ascot 2013 - as she toured the show, which she has visited every year for half a century.
Heavy showers had struck in the morning, but the dark clouds parted and the sun shone as the royals arrived.
The Queen was shown a 30ft tall sculpture of ceramic tulips made by Paul Cummins, the artist behind last year's poppy display at the Tower of London.
She said the piece was "extraordinary" as she chatted to the sculptor for a few minutes.
Charles and Camilla toured the show with her sister Annabel Elliot and her husband Simon.
The Princess Royal, the Earl and Countess of Wessex, the Duke and Duchess of Gloucester and Prince and Princess Michael of Kent also attended the show.
Harry told earlier how he was still waiting to be introduced to his new niece.
He revealed he had still not met Princess Charlotte, who was born while he was away on a four-week attachment to the Australian Defence Force.
Asked on BBC Breakfast about meeting the baby, he said: " That still hasn't happened yet. I only got back yesterday afternoon. Time will tell when I have a chance."
Home-grown talent is vying with designers from as far afield as Australia and Dubai to win the title of best show garden at the exhibition.
Harry took an extensive tour, stopping off at several gardens and exhibits to look at the flowers.
As he was shown around the garden created for his charity, he spent a few minutes having a guided tour and chatting about it.
A Basothu choir dressed in colourful traditional outfits sang for him as he left the garden.
Smiling, Harry shook each of their hands and chatted to the choir as he left.
The garden features bright flowers of oranges and reds, plants native to the small African country, and a waterfall to echo the nation's oases.
Harry said the garden was "fantastic" and "everything I could have wished for".
"From all the sketches of what it would look like, this is exactly how I imagined it," he said.
"It's kind of perfect. If my garden was big enough, I would try and move it into my garden."
The Prince said parts of it were "exactly like Africa".
"I'm aware lots of people haven't been to Africa, let alone Lesotho," he added. "This is our way of bringing a little bit of Lesotho to Chelsea."
For the first time in the show's century-long history, an amateur will compete with professionals for the award.
Sean Murray, a nurse from Ashington in Northumberland, claimed his spot on the main bloom-lined boulevard after winning the BBC's Great Chelsea Garden Challenge.
Beaming as he stood next to his garden with a yellow rose stuck on his jacket, he said it was an honour to be at the show.
He said: "To think that this design was in my head, then on paper, seeing it transformed into a living, breathing space as a garden, is incredible.
"And to know that one of our longest reigning monarchs is seeing it is a great privilege and honour. This is a life defining moment."
The Royal Bank of Canada announced that its garden at the show is to be donated and relocated to Earl Mountbatten Hospice on the Isle of Wight.
The show garden, designed by Matthew Wilson, managing director and principal designer of Clifton Nurseries in London, aims to reflect the bank's commitment to help protect the world's fresh water resources, highlighting urban water management and water saving solutions for gardens.
After Chelsea, the garden will be rebuilt with the help of charity Greenfingers, becoming part of a project to expand children's services at the hospice in Newport and give youngsters with life-limiting conditions and their families more outdoor facilities.