Foreign Secretary Dominic Raab has told a virtual Conservative conference he feared Boris Johnson could have died of coronavirus.
Mr Raab stood in for the prime minister after Mr Johnson was admitted to intensive care following his COVID-19 diagnosis in the spring.
Watched on screens by delegates, the First Secretary of State told the conference: “It nearly took the life of our prime minister, our friend as well as our leader.
“I get asked a lot how I felt, when I covered for him.
“Well, I really worried we might lose him, and I was worried for Carrie (Symonds), pregnant with baby Wilf.
“But I always had faith that with the outstanding NHS care he received and his fighting spirit, he’d pull through.”
As US President Donald Trump was being treated in hospital after becoming infected with the virus, Mr Raab revealed he was anxious Mr Johnson could have been one of the tens of thousands killed by the illness in the UK.
Mr Johnson admitted, after his release from hospital on Easter Sunday, that his life had been in peril, saying “it could have gone either way”.
He has since tried to lose weight, having found out it is those who are obese who are more at risk.
In an interview with the Daily Telegraph, the prime minister said he had lost almost two stone.
“I try not to eat too much sometimes, and it’s basically about taking lots of exercise and not eating so much,” he told the paper.
He also told the BBC that claims he was planning to step down next year were “sinister disinformation”.
Rumours circulated over the last few months that the prime minister would not see out a full-term in office because he was struggling in the wake of his coronavirus battle.
During his conference speech, Mr Raab said he felt the need to pray that the country would be “equal” to the “greatest challenge in a generation” as the pandemic took hold.
He admitted there were “lessons to be learnt” in the wake of the crisis, and added: “I have to say, for every hurdle we faced, with every heart-rending loss, there was also a tale of courage, a moment of inspiration.”
Cabinet Office minister Michael Gove, also speaking at the Tory Party conference, said the Conservative leader had made an “amazing recovery” and said the prime minister was the “livest wire in the room”.
Mr Gove used his conference speech to add that he wants to move large government departments out of London to support Boris Johnson’s so-called “levelling-up” agenda.
He said it is time for civil servants to be “closer to where the action is”, and he argued home-working during the pandemic proves the upheaval can work.
The virtual Conservative conference opened on Saturday, with the announcement that the party plans to open a second headquarters in Leeds in a bid to “show our commitment to the blue wall seats”, co-party chairman Amanda Milling said.
She added the aim was to have the headquarters open next year. Mr Gove has said the Civil Service should follow suit as the party looks to create jobs outside of London.