After a day in a strange vacuum, an official statement emerged from Downing Street just after 20:00 BST.
Having struggled to shake off symptoms, and having been taken to hospital 24 hours before, No 10 announced that the prime minister had been moved into intensive care.
Downing Street has made clear that Boris Johnson is still conscious, and it is understood that he has not yet received any kind of ventilation to help him breathe.
But the decision was taken to move him to part of St Thomas' Hospital, where that kind of treatment would be immediately available if required.
It has been clear for many days that Mr Johnson was taking far longer to recover than had initially been expected.
He regularly popped up on social media to say that he was suffering mild symptoms and was following advice in customary bombastic tone.
Even this morning No 10 was insisting that he was still receiving red boxes full of government business and was in touch with his team.
But obviously, with his condition deteriorating on Monday afternoon, the view of his condition changed.
With the prognosis uncertain, the government has taken a highly unusual move of asking Foreign Secretary Dominic Raab to step up to deputise for the prime minister when needed.
Talking on Monday night, he said that the government's business would go on, ministers focused on delivering the plans to tackle coronavirus that Mr Johnson had instructed them to do.
But the foreign secretary seemed understandably, but obviously, shocked.
Politicians have repeatedly said that coronavirus does not discriminate, the infection does not pick and choose.
With Boris Johnson now in intensive care, it is abundantly clear that power is no protection from harm.