“We are sending Prince George a beautiful, bouncing blue tricycle to get him on a bike at the earliest possible opportunity and to acculturate him to the joy of cycling,” Mr Johnson revealed during his monthly radio phone-in.
The mayor admitted on LBC 97.3 he was unclear about the details of the gift – which is being custom-made for the son of the Duke and Duchess of Cambridge, who was born last month.
However, he said it “might well be” in the style of the blue bicycles, nicknamed “Boris Bikes”, which are available for public hire in London.
The gift came as the mayor defended a cycling festival which took place in London on Sunday amid complaints from drivers about road closures.
Prince George was sent a soft toy as a gift from “the people of Scotland”, and two charities will also receive £25,000 donations to celebrate his birth, First Minister Alex Salmond revealed.
Prime Minister David Cameron gave Prince George a box-set of books by Roald Dahl.
Liberal Democrat leader Nick Clegg and his wife Miriam sent the duke and duchess a big bag of coffee to help them cope with sleepless nights, along with a white cot cover and sheet hand-embroidered by nuns in Mrs Clegg’s home village in Spain.
Labour leader Ed Miliband sent a three-year-old apple tree – a traditional gift for a first-born boy.