The couple, their one-year-old son Prince George and the new arrival were to spend time relaxing together at their Kensington Palace apartment, the day after Kate gave birth to a baby girl born fourth in line to the throne.
The beaming Duke and Duchess of Cambridge left hospital Saturday carrying their newborn princess in front of hundreds of cheering well-wishers and the massed ranks of photographers from the world's media.
The sleeping baby was wrapped in a woollen shawl as a relaxed-looking Kate, 33, cradled her in her arms in front of the private Lindo Wing of St Mary's Hospital in central London.
William, 32, then drove his wife and daughter the short distance to Kensington Palace after carrying the baby out in a car seat.
The family of four may be in for some special visits Sunday from their nearest and dearest.
Royal watchers will be keeping alert for first visits from William's father Prince Charles and his wife Camilla, and from Kate's parents, Michael and Carole Middleton.
William's grandparents Queen Elizabeth II and her husband Prince Philip will also be eager for a first glimpse of their fifth great-grandchild.