UK's Prime Minister, Boris Johnson and Carrie Symonds are engaged and expecting a baby

55-year-old UK Prime Minister, Boris Johnson and his 31-year-old girlfriend Carrie Symonds are engaged and are expecting a baby together.

The couple who reportedly got engaged at the end of last year, confirmed they are expecting a baby via a social media post.

In her private Instagram account, Carrie Symonds wrote:

    "Many of you already know but for my friends that still don't, we got engaged at the end of last year... and we've got a baby hatching early summer. Feel incredibly blessed."

Johnson and Symonds became the first unmarried couple to occupy Downing Street when they moved in last year.

Symonds who has also enjoyed a successful political career, is the youngest partner of a prime minister in 174 years. She worked as part of the campaign team that helped to get Johnson re-elected as mayor of London in 2012.

This will be the third marriage for Mr Johnson - who divorced his first wife and is now estranged from second wife Marina Wheeler who he already has four children with.

The last time a child was born to a sitting UK prime minister was in 2010, when David Cameron and his wife Samantha Cameron, welcomed their daughter Florence.