The black and white photograph shows Prince William in a flat cap, holding his youngest son, one-year-old Prince Louis, close and giving him a kiss on the cheek.
The royals posted the photograph – taken by Kate in Norfolk earlier this year – on their official Twitter account Wednesday with the caption: “Merry Christmas to all our followers!”
It also shows a smiling Prince George, 6, sitting in a chair next to his dad and brother, while his sister, four-year-old Princess Charlotte stands behind.
The Cambridge’s two eldest children were expected to attend the royal’s annual Christmas day church service at Sandringham for the first time on Wednesday.
This is not the first time Kate has shared her own family photographs with the world.
Earlier this week, William’s brother Harry released his first family Christmas card featuring his wife, Meghan and baby Archie. The adorable eight-month-old tot was seen front and center, staring into the camera.