Both photos were snapped by Middleton, who has taken to releasing images of her children to celebrate important milestones in their lives, such as the first days of nursery school for both Prince George and Princess Charlotte.
The two snapshots were released by Prince William and his wife Kate, the Duchess of Cambridge, and were taken by Kate at their home in Kensington Palace.
George, 4, previously wore the sweater from Spanish brand Fina Ejerique, which retailed for US$52, in a 2016 photo of Queen Elizabeth with seven of her grandchildren and great-grandchildren.
Prince Louis, the third child of Kate Middleton and Prince William, was born on April 23, and just hours after this birth, the proud mom and dad posed for photos outside of the hospital with their latest bundle of joy. The second photo, taken on Princess Charlotte's third birthday on May 2, shows the older sister planting a gentle kiss on her baby brother's forehead.
Prince Louis made his portrait debut!
The Duchess of Cambridge was also the one who documented Princess Charlotte's first days at the Kensington Palace three years ago.
Prince George holding Princess Charlotte in 2015.
Then, Princess Charlotte celebrated her birthday.
"The Duke and Duchess would like to thank members of the public for their kind messages following the birth of Prince Louis, and for Princess Charlotte's third birthday", a statement shared with the image on the official Kensington Palace Instagram. The palace has already announced that Prince Louis will not attend the royal wedding of Prince Harry and Meghan Markle on May 19.