Boris Johnson's sister-in-law has tonight said she has also tested positive for Covid-19.
Gabriela Maia, who is married to Boris's financier half-brother, Max, said she is "still recovering from the virus with some respiratory difficulties".
The 30-year-old, who is pregnant, told the Daily Mail: "I am OK now and I just feel so lucky to be alive and I pray that my baby is safe.
"My heart just melts for the ones who haven't been so lucky. It's really, really sad."
It comes after Boris Johnson shared a video message on Twitter this morning confirming he had contracted the virus.
He said: "Over the last 24 hours I have developed mild symptoms and tested positive for coronavirus."
He added: "I am now self-isolating, but I will continue to lead the government's response via video-conference as we fight this virus."
Carrie Symonds, the PM's fiancee - who is pregnant - is at their Camberwell home after leaving No11 a few days ago, The Sun reports.
The 32-year-old, who was last seen in public with Boris on March 9 at the Commonwealth Service at Westminster Abbey, last night confirmed she was self-isolating amid the pandemic.
Pregnant women are considered one of the categories at risk for the bug.
Health Secretary Matt Hancock confirmed today he also tested positive for Covid-19.
Chris Whitty, the Government's Chief Medical Officer, said he has also been forced to self-isolate after suffering from coronavirus symptoms.
In the UK, there are more than 14,500 confirmed cases of Covid-19 and at least 759 people have died.
