The Royal couple left baby Prince George at home and travelled by bus to surprise hundreds of commuters at an Underground station to support London Poppy Day with EastEnders' actress Barbara Windsor and newsreader Alastair Stewart.
When asked about George, Kate said "He's half asleep,' with William adding: "He's behaving himself this morning."
Organisers are aiming to raise more than £1 million in a single day. All funds will go towards the national Poppy Appeal fund-raising target of £37 million to allow the Royal British Legion to carry out its vital work.