Princess Charlotte is seen cuddling the sleeping prince in the photo taken on May 2, her third birthday, the BBC reported.
A second picture shows Prince Louis on April 26, when he was three days old, propped on top of a white cushion.
Both photos were taken by the Duchess of Cambridge at Kensington Palace.
Catherine also released pictures to mark other milestones in her children's lives, including the official photographs of her newborn daughter and Prince George and Princess Charlotte's first days at nursery school.
Kensington Palace said Prince William and Catherine were "very pleased" to share the photographs.
"Their Royal Highnesses would like to thank members of the public for all of the kind messages they have received following the birth of Prince Louis, and for Princess Charlotte's third birthday."
Prince Louis was born at the Lindo Wing of St Mary's Hospital, Paddington, on April 23.
Prince George, who will turn five in July, does not appear in the latest photographs, reports the BBC.
He was last seen in public outside St Mary's Hospital when he and Princess Charlotte were taken by their father to meet the latest addition to their family.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
