Ismail Mohamed Abdulwahab, 13, and Luca Di Nicola, 19, both passed away having picked up the deadly virus.
Ismail, a schoolboy from Brixton, started showing symptoms and had trouble breathing on Thursday so was rushed to hospital, his relatives said.
They told how he tested positive for the disease the following day and was put on a ventilator then into an induced coma – but he died in the early hours of Monday at King’s College Hospital.
COVID-19 is so infectious that his family could not be with him when he died.
“We are beyond devastated,” a statement released through a family friend said.
“To our knowledge he had no underlying health conditions.”
Mr Di Nicola, an assistant chef from Nereto in central Italy, was also called “very healthy” by his family, and the NHS confirmed he had no underlying health conditions.
He was taken by ambulance to the North Middlesex Hospital in Enfield, north London, last Tuesday – but died 30 minutes later, from apparent fulminant pneumonia.
Luca Di Nicola
Luca’s father, Mirko, told La Repubblica that his son had contracted the virus, and that the family received an email from British medical authorities saying a post-mortem swab had confirmed that.
It is believed the coroner has not officially confirmed it.
The government’s latest daily announcement said 393 more people have died after catching coronavirus – taking the UK total to 1,808.
A 12-year-old girl in Belgium is the youngest known person to die in Europe after catching coronavirus.
Doctors have warned that while older people with health problems are at particular risk of COVID-19, that does not mean young people will be unaffected.