Watch: Duchess of Cambridge launches Hold Still: A Portrait Of Our Nation photo book
Prince Louis is "very quick running around" and loves his scooter and bicycle, the Duchess of Cambridge has revealed.
Kate was speaking on a call with one of the entrants of her photography project Hold Still, which captured the UK in lockdown last Spring.
She spoke to Mila Sneddon, who is now five and the subject of one of the images, in a call shared online a few days before the book's release.
Mila proudly told the duchess she knew the names of her children, proceeding to list Charlotte, then George and Louis, prompting the update from Kate.
Kate said: "Louis has got so big now, he's very quick running around and he's on his little scooter as well.
"He's very quick, I can't keep up with him."
Louis turned three on 23 April and his birthday was marked with a new image of the prince on his balance bike, before his first day at Nursery at Willcocks in Kensington.
It was the start of a string of new family photos and videos from the Cambridges, with the pictures of Louis and his sister Charlotte taken by Kate, who is a keen amateur photographer.
It was her passion for photography that inspired the Hold Still project, and a photo-book of 100 of the entrants, including the picture of Mila, is out on Friday.
Mila's parents made the difficult decision before the lockdown began in March 2020 to live separately to protect the five-year-old, who was receiving chemotherapy for acute lymphoblastic leukaemia.
For her safety, Mila’s father, Scott, and big sister, Jodi, had to live separately from Mila and her mother Lynda until he was furloughed from work.
Sneddon took a picture of her daughter Mila kissing the kitchen window as she looked out to see her father who was keeping away to protect her.
Kate told Sneddon: "We love your photograph."
The call began with Mila answering the phone and saying: "Good morning your royal highness”, with Kate replying: “Good morning. Goodness me, you’re so polite Mila.”
The duchess and Mila, who was four when she spoke to the royal, talked about how difficult it had been to be separated from her father and the moment they were reunited.
Mila said: "When he came into the house I was like, so surprised."
The little girl also asked the royal if she had a costume, to which Kate replied: "I’m not wearing a princess costume right now, I’m afraid Mila. Do you have lots of dressing-up outfits yourself?"
Mila said "yeah" and went onto tell the duchess her favourite colour was pink.
Kate said: "OK, well I have to make sure I go and try and find myself a pink dress so that when one day hopefully, Mila, we’ll get to meet and then I’ll remember to wear my pink dress for you. Would that be nice?"
The full call was shared on the new Duke and Duchess of Cambridge YouTube channel, which was launched on Wednesday afternoon.
The call was not filmed so the audio was overlaid with pictures of Mila in hospital, the photo from the exhibition and stills of the duchess on the phone.
On social media, Kensington Palace explained the call took place last autumn.
The Duke and Duchess of Cambridge launched their YouTube channel on Wednesday afternoon, picking up more than 244,000 subscribers within 24 hours.
Watch: Prince William and Duchess Catherine launch YouTube channel!