What has Johnson said about his departure?
Johnson has told Sir Graham that he will announce his resignation on Thursday so that there can be a new prime minister in time for the Tory conference.
The annual gathering of the revelers will take place in Birmingham this year and will begin on October 2.
What will happen now that he has resigned?
There will be now a leadership contest to replace Mr Johnson as leader of the Conservative Party and as Prime Minister.
The Prime Minister’s comments suggest that he, like his predecessors Theresa May and David Cameron, will remain in office while the party elects its new supremo.
Tory leadership battles usually take two months to complete and take place over two rounds.
First, a longlist of MPs is drawn up by Tory party leaderswith only those who had received the support of at least eight of their colleagues making the final move.
They then go into two grueling rounds of selection, with the first seeing all Tory MPs vote in three consecutive rounds to narrow the candidates down to a final two.
Hopeful people need the support of at least 5 percent of the parliamentary party, or 18 MPs, to get through the first phase and 10 percent, which is equivalent to 36 MPs, to make it through the second.
It is then up to the 200,000-strong party members to choose between the remaining pair after several weeks of arduous campaigning and hustings debates.
Who will replace Boris Johnson?
The race to replace Mr Johnson is expected to be a busy field, with cabinet ministers pitted against heavyweight backbenchers.
Attorney General Suella Braveman has already announced her intention to run for office and is expected to be followed by many of the prime minister’s top team.