Prime Minister Sir Keir Starmer has paid tribute to his younger brother Nick, who had cancer, after he died on Boxing Day at the age of 60.
"My brother Nick was a wonderful man," Starmer said in a statement.
"He met all the challenges life threw at him with courage and good humour. We will miss him very much."
It is understood Starmer had been planning to go on holiday but will now stay behind.
"I would like to thank all those who treated and took care of Nick," Starmer added.
"Their skill and compassion is very much appreciated."
Conservative leader Kemi Badenoch expressed her condolences to the Labour leader.
"This is such awful news. Particularly devastating at Christmas time," she wrote on X.
Nick Starmer had learning disabilities from complications during birth and struggled to hold down a steady job.
In a biography of the prime minister published this year, Keir Starmer opened up about his relationship with his brother and the difficulties he faced during his childhood.
"I'm not sure he even sat exams, so he had nothing to show for coming out of education," Starmer told author Tom Baldwin. He said his brother was bullied and was often called "thick" or "stupid" at school.
"Nick was dealt a very different set of cards to me and he's had problems all his life - problems I've never had to face," Starmer said.
In his speech to the Labour Party conference in September, he said their father had often told him that "your brother has achieved just as much as you, Keir".