The reason behind the Duchess of Cambridge’s surprise visit to a children’s art therapy centre in Holloway has been revealed.

Her Royal Highness made an informal visit to the The Art Room at the Robert Blair Primary School in Brewery Road, back in November.

And it was announced on Thursday last week that she had chosen to become a patron of the organisation, which runs several similar centres.

It uses art therapy to help children aged five to 16 with issues such as low self-esteem and Asperger’s syndrome.

The Princess, who had spent months researching the charitable sector, dropped in on a session in Holloway and watched as children painted underwater creatures onto the seats of chairs.

Headteacher of Robert Blair Primary School, Mark Miller, who secured funding for the facility after visiting another centre in Oxford, said: “She asked to come and spend the morning in the art room as a volunteer helping out.

“Somebody said to one of her representatives to dress accordingly as we get a bit messy here with all the paint, but it was still a surprise seeing her step out of the car wearing jeans, black boots and a jumper.”

He continued: “She was charming. We chatted to her for a little while about our work, even though she was very well informed already.

“She then literally spent one-and-a-half hours with a group of children as one of the helpers. The children loved her – some knew exactly who she was and others didn’t, but they all thought she was great.

“She did a history of art degree and she is obviously interested in helping children, and particularly children that are maybe from slightly more difficult backgrounds and finding learning or life more difficult than she did as a child. So the Art Room combines two of her big interests.”

Mr Miller said the announcement was brilliant news for the school and the charity, and he is hoping for more royal visits in the coming years.

Juli Beattie, founder and director of The Art Room, said: “We hope this amazing patronage will make it possible to open every art room five days a week and reach many more children – it really does work.”