Britain's royal family on Sunday released two pictures of its newest arrival, Prince Louis, taken by his mother Kate at their Kensington Palace home.
In one touching image, 3-year-old Princess Charlotte is kissing her sleeping brother, while the other shows the royal baby propped against a cushion.
"The Duke and Duchess of Cambridge are very pleased to share two photographs of Princess Charlotte and Prince Louis," said a Kensington Palace statement.
The image with Princess Charlotte was taken on May 2 - her third birthday - while the other, in which Louis wears a white jumper and trousers, was taken on April 26, three days after he was born.
Louis Arthur Charles, fifth in line to the British throne, is William and Kate's third child and the sixth great-grandchild for Queen Elizabeth and her husband Prince Philip.
His name was announced on April 27, five days after his birth.
The first photograph, which the palace said was taken on April 26, shows Louis propped up against a white cushion, wearing a white jumper and trousers.
The second photograph, taken on May 2, Charlotte’s third birthday, shows the princess holding her sleeping younger brother affectionately.
Due to a 2013 change in the law, Charlotte is the first British princess for whom the arrival of a younger brother does not mean being demoted down the line of succession.
He will hold the title of prince after the Queen changed the rules in 2012 to ensure that all of William's children would be entitled to the style, not just his eldest son.
The birth kicks off a busy summer of royal celebrations, with Prince Harry set to marry US actress Meghan Markle on May 19.