Little did the world know then that there was double cause for celebration for Carrie Symonds behind Downing Street's black door.
Boris Johnson and Carrie Symonds have announced they are expecting their first child, due in the summer this year after the couple marries in a spring ceremony.
But it was not until six months later, in September 2018, that the pair were romantically linked, after it was announced Mr Johnson had separated "some months ago" from Marina Wheeler, his wife of 25 years and mother of four of his children.
He and Symonds have already made history as the first unmarried couple to occupy the prime minister's official residence.
It will be the first child for Symonds, who previously worked as a communications chief for Johnson's Conservative Party. 29, 2020 he and his girlfriend Carrie Symonds are expecting a baby in the early summer and are planning to get married.
Symonds, 31, has also enjoyed a successful political career, working as part of the campaign team that helped to get Johnson re-elected as mayor of London in 2012.
Prime Minister Boris Johnson kisses his partner Carrie Symonds on the cheek after delivering his speech during the Conservative Party Conference at the Manchester Convention Centre, Britain, 2 October 2019.
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The party is now represented in all 16 German state legislatures and in some parts of the country polls in double digits. The breach of a historic political taboo provoked a nationwide backlash against both mainstream right-of-centre parties.
The baby will be Symonds' first, but it's not so clear-cut for Johnson.
A family court judge approved a financial settlement and gave Ms Wheeler permission to apply for a divorce decree.
Mr Johnson met his first wife, Allegra Mostyn-Owen, while they were students at Oxford.
The marriage was annulled in 1993 and he Wednesday Ms Wheeler later that year.
There has been speculation that Mr Johnson has fathered another extra-marital child.
In 2004, he was sacked from the Tory frontbench over a reported affair with journalist Petronella Wyatt.