UK Prime Minister Boris Johnson and fiancée Carrie Symonds welcome baby boy

UK Prime Minister Boris Johnson and his fiancée Carrie Symonds have announced the birth of a "healthy baby boy at a London hospital earlier this morning".

Both mum and baby are doing well, a spokesperson said in a statement announcing the news.

"The PM and Ms Symonds would like to thank the fantastic NHS maternity team," they added.

The Queen has reportedly sent a private message of congratulations to the happy couple.

The news comes just a day after the Prime Minister returned to work following his battle with COVID-19, which left him in intensive care for three days.

According to British media reports, Mr Johnson had originally suggested he intended to take paternity leave when the baby arrives but it's not known if this is still the case, given the coronavirus crisis.

The 55-year-old is only the fourth prime minister to welcome a baby while in office in 170 years.

Ms Symonds is the first partner of a serving prime minister in Downing Street to become a first-time mum. The 32-year-old is also the first unmarried spouse of a prime minister to live at No.10.

In February, Mr Johnson and Ms Symonds announced they had gotten engaged in December and were expecting a child together in the UK summer.

The former Mayor of London has been married twice before and has four children with his second wife, Marina Wheeler.

Mr Johnson also allegedly fathered a daughter during an extramarital affair with art consultant Helen Macintyre in 2009, while still Mayor of London, according to court documents in 2013 referenced by The Guardian. However, he has never publicly commented on this.