Boris Johnson after winning the Tory leadership race on Tuesday (Picture: PA).
Boris Johnson will take up office as Prime Minister of the United Kingdom on Wednesday, after having beaten rival Jeremy Hunt in the Conservative leadership race.
Mr Johnson will have much on his plate over the coming weeks and months, after moving into Downing Street.
But what will be his first priorities in the role, and how is the handover between Theresa May and Mr Johnson managed?
It is a highly choreographed day of ceremony, up to a point.
After a farewell lunch at Number 10, Theresa May will say her final goodbyes to Downing Street staff and give a final speech before heading to Buckingham Palace for her formal resignation to the Queen.
Then Boris Johnson will go to the palace, for his formal invitation to become Her Majesty’s Prime Minister.
On leaving the Palace, he will be driven to Downing Street where he is expected to make a speech in front of the world’s media.
Then he will walk into Number 10, which is where the ceremony is over and the hard work begins.
The Chief of Defence Staff, and three service chiefs will be waiting for Mr Johnson in the cabinet room, to brief him on threats to the UK, and current UK military deployments around the globe, including special forces.
Mr Johnson will then have to make what could be the most important decision of his leadership when he writes the letters of last resort.
Kept in the safes of Britain’s nuclear armed submarines, they are instructions to the boat's captains are only to be opened and acted on in the event of a military strike that leaves the UK with no government.
The letters Theresa May wrote will be destroyed, without ever being read.
After the national security duties are done, Boris Johnson will likely turn his focus on shaping his cabinet.
Theresa May has made clear she wants the government to put more money into defence, writing an article in the Daily Telegraph, saying the UK has repeatedly failed to deliver on the military capability plans it has set out in defence reviews.