Prince William and Catherine, Duchess of Cambridge have released a new picture of their youngest child, Prince Louis, to mark his third birthday, and his first day at preschool.

The image, taken by Catherine at Kensington Palace on Wednesday, shows a smiling Louis on a red bike, shortly before heading off for his first day at the Willcocks Nursery School.

The school, founded in 1964, is housed in a church hall just a short walk from Kensington Palace and was also attended by Louis' sister, Princess Charlotte.

It charges up to £10,200 (around US$14,000) a year for morning attendance.

Louis was born on April 23, 2018, becoming fifth in line to the throne behind his older siblings, Prince George and Princess Charlotte.