Conservative leader David Cameron's eldest son Ivan, who had cerebral palsy and epilepsy, died in the early hours of Wednesday.
The six-year-old, who his father described as "wonderful", became ill overnight and was taken to St Mary's hospital in London where he later died.
The Conservative leader chose to be open about his son's disability and the whole family were shown together in a portrait taken for the Cameron's Christmas card.
Mr Cameron, who has been leader of the UK's official opposition since 2005, had been an MP for less than a year when Ivan was born in April 2002.
The Conservative leader says he stills baths his children at least once a week. Here, Mr Cameron, Ivan (left) and his brother Arthur are seen at a Christmas Day service with the Archbishop of York.
Ivan and Samantha Cameron are seen here at the opening of a new lift to enable children in wheelchairs to access a yoga centre in London.
Describing the moment when he learned of Ivan's disabilities, Mr Cameron told the Sunday Times in 2005: "The news hits you like a freight train."
David and Samantha Cameron have passed on their thanks for the messages of support after the death of son Ivan, their "beautiful boy".