Doting big brother, Prince George, placed a gentle kiss on his newborn sister, Princess Charlotte's forehead not long after her birth in 2015.
Photo: Duchess of Cambridge
The little Prince proudly held on to his baby sister, while sitting on a couch, for their first portraits together.
Photo: Duchess of Cambridge
George was one happy older brother sitting perched up with Princess Charlotte in his arms at their family's country home Anmer Hall.
Photo: Duchess of Cambridge
Big brother's looking out! George peered into his sister's pram at her July 2015 christening held at the St. Mary Magdalene's church.
Photo: Matt Dunham - WPA Pool/Getty Images
Season's greeting from the Cambridges! The little family posed for a sweet photo together in 2015. Attached to the portrait a message read: "The Duke and Duchess are hugely appreciative of all the warm messages they have received about their family this year and are very much looking forward to their first Christmas as a family of four."
Photo: Chris Jelf
Charlotte and George were a pair of adorable snow bunnies, while on a ski holiday in the French Alps with their parents.
Photo: John Stillwell - WPA Pool/Getty Images
The royal siblings had fun in the snow during their family vacation in France.
Photo: John Stillwell - WPA Pool/Getty Images
Prince George and Princess Charlotte hammed it up for the cameras, smiling and waving from the balcony of Buckingham Palace during the 2016 Trooping the Colour.
Photo: Samir Hussein/WireImage
The royal brother and sister made the same gesture and face as their mother pointed out to the distance during the Trooping the Colour.
Photo: Samir Hussein/WireImage
Charlotte and George both gazed up to watch the RAF fly over Buckingham Palace.
Photo: Samir Hussein/WireImage
The Duke and Duchess of Cambridge's children were joined by their cousins at Windsor Castle for a photo with their great-grandmother, Queen Elizabeth, in honor of her 90th birthday.
Photo: Annie Leibovitz/Getty Images
Charlotte had her parents and brother George by her side as she embarked on her first royal tour of Canada in 2016.
Photo: Karwai Tang/WireImage
The Cambridge siblings appeared intrigued by their new surrounding while on the tarmac of Canada's Victoria Airport, where they were beginning their royal tour of the North American country.
Photo: Karwai Tang/WireImage
George got his hands on an orange bubble gun toy, which he use to squirt bubbles at his sister and father during a children's party in Victoria, Canada.
Photo: Chris Jackson / PA Wire/Press Association Images
The siblings played with their stylish mother and balloons at a party thrown in their honor during the Cambridge family's royal tour of Canada.
Photo: Chris Jackson / PA Wire/Press Association Images
The royal youngsters were amused by balloons and even pulled uninflated ones from the party entertainer's pouch.
Photo: Chris Jackson / PA Wire/Press Association Images
Charlotte and George attentively watched an entertainer make whimsical balloons for them.
Photo: Chris Jackson / PA Wire/Press Association Images
The royal tots were joined by their parents for playtime during a children's party for military families at Victoria's Government House.
Photo: Chris Jackson / PA Wire/Press Association Images
George and Charlotte coordinated with their parents Prince William and Kate Middleton during Christmas Day service at St. Marks church Bucklebury, Berkshire in 2016.
Photo: Andrew Matthews PA Wire/PA Images