And alongside the Princesses at the unveiling of The Great North Children's Hospital unit was X Factor winner Joe McElderry.
The local singer joined the royal guests, as well as legendary Who frontman Roger Daltrey, to chat to youngsters benefiting from the facility at the unveiling.
Like their mum, both Beatrice and Eugenie, who wore complementary green and blue dresses for the visit, are keen supporters of the Teenage Cancer Trust.
The Duchess first got involved with the Trust 20 years ago and has opened 15 such units since then.
“As a parent to two young and fortunately healthy girls, this charity has a particular place in my heart," she said.
“Over the past 20 years, I have seen how important these specialist units are to a young person going through cancer treatment.”
The new £1.7 million facility, situated near where Eugenie is studying at Newcastle University, has been designed with teenagers in mind.
It includes a recreational room, kitchen and dining area, a study, parents' room, a complementary therapy room and chill-out zone, plus access to the internet and music.