Candid William reveals he wants two babies with Kate

William has spoken candidly in the past about starting a family with Kate but had not commented about numbers.

His admission came during a visit to the Gardens by the Bay attraction in Singapore on a walkabout.

Corine Ackermann, 17, who was with school friends from the Tanglin Trust British School, said: “Someone asked him how many children he would like to have, and he said he was thinking about having two.”

The Duke has mentioned a number of times his desire to start a family and it is not unusual for members of the public to quiz him about the topic.

When interviewed by ABC broadcaster Katie Couric earlier this year William highlighted the importance of raising a family.

Speaking about his RAF career, he said he loved being in the Armed Forces but “the pressures of my other life are building”, and went on to say: “More importantly, I’d like to have children”.

He added: “I’m just very keen to have a family and both Catherine and I are looking forward to having a family in the future.”

The Duke was asked if there was anything he would like to announce and replied: “You won’t get anything out of me. Tight-lipped.”

As they chatted to crowds Jaz Heber Percy, 13, asked the Duke what superpower he would like to have if he could be a superhero.

The Duke replied: “That’s a hard question – I’m not sure. I’ll have to think about it. I think invisibility.”

Her friend Charlotte Phillipson, 13, burst into tears when the Duchess spoke to her: “She is my idol, she is a great model and something really to aspire to. ”

During the visit to the gardens, which have two Eden Project-style domes housing rainforest plants, the Duke and Duchess planted a pachira glabra variegata tree to mark their visit.