Kate said this was “very cool”, and joked that she might have to get the Duke of Cambridge the Spider-Man costume.
“I’ll see if it takes on the trend here at Kensington Palace,” she said.
“Unfortunately I’m not so sure if he’s going to get the air clearance that you’ve got.”
Sunrise royal correspondent Peter Ford said: “She said to the little sick girl, I’ll meet you and wear a pink dress and said about William, I’ll buy him the costume and put it on him. She’s got to go through with it now.”
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.
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.