Gordon Brown's wife Sarah is pregnant and expecting the baby in July, a spokesman for the Chancellor said today.
The spokesman added: "Sarah and Gordon are absolutely delighted by the news."
The couple have a two-year-old son John. Their baby daughter, Jennifer Jane, died after being born prematurely.
Jennifer Jane, who was born seven weeks early, died in January 2002 aged just 10 days.
She weighed 2lb 4oz and died in Edinburgh Royal Infirmary, having spent all of her short life in hospital.
Speaking after her death, Mr Brown said that the little girl had been an "inspiration" to him and his wife, adding: "I don't think we'll be the same again."
He said later he could not listen to music for nearly a year after Jennifer Jane died, but he and Sarah had taken comfort from the thousands of letters they received from other couples who had suffered similar experiences.
In April 2003, the Browns announced the happy news that they were expecting another child.
Their son John, named after the politician's paternal grandfather, was born in October 2003, weighing 8lb 1oz.
The Chancellor pronounced himself part of the "happiest family in Britain".
He spoke later of how much he was enjoying being a father.
"There are sleepless nights but there is a spring in my step every morning," he said.
Mr and Mrs Brown married in 2000.