Kate proved true to her word when she invited little Mila Sneddon and her family to the Queen's official Edinburgh home and wore an ME+EM outfit that matched the five-year-old's dress.
The outgoing little girl, who is battling cancer, has captured the duchess' heart - and when they met she told the youngster she wanted to give her a "big squeezy cuddle".
Mila was featured in a picture from Kate's lockdown photographic project and came to symbolise isolation during the pandemic after she was pictured kissing her home's kitchen window as her father stood outside.
The little girl is undergoing chemotherapy for leukaemia and was photographed separated from her father during the first lockdown, after he had to go to work and could not risk bringing coronavirus into the family home in Falkirk.
Kate and Mila had talked on the phone after the image was among 100 selected for the duchess' Hold Still exhibition and book, and agreed to meet up.
The pair met at the Palace of Holyroodhouse and when Kate walked into the room, the face of the little girl it up.
"Hi Mila, look at you. I want to give you a big squeezy cuddle, it's so nice to meet you in person," Kate said.
The five-year-old stood up as did her father and mother, Scott and Lynda Sneddon, and her big sister Jodi.
Kate praised the little girl who was dressed head-to-toe in pink with matching headband, dress and shoes.
She said: "I love your dress, can you do a little twirl - and your shoes."
Mila spun round for the future queen before running over to her father.
She was not phased by meeting royalty and later her mother, who described the experience of chatting to Kate as "surreal", said the five-year-old did a handstand and cartwheel in front of the duchess.
The youngster understands about the effects the pandemic has had on her family life, and after meeting Kate described the story behind her Hold Still picture taken by her mother: "It's because daddy had to self-isolate to keep me safe from the coronavirus and then he finally came back home."
Mr Sneddon isolated from his daughter as a precaution, as in the early period of the pandemic it was not clear the effect the virus had on children - but after seven weeks was able to return home.
When Mila was asked about what she and the duchess spoke about, she replied: "Well I was busy drawing a picture - a robot."
But she liked Kate's pink dress and said about the experience: "It was so good, I've never met a real princess in my life before."
There was an exchange of gifts with Kate giving the little girl a tiny trinket box inscribed with a message about bravery while the duchess' young friend presented her with a candle and a bag.
Mrs Sneddon said: "It's a really surreal and bizarre experience, we've come out of lockdown and this is our first trip out which is really unusual."
Reporting by PA