Suella Braverman has resigned as home secretary after only six weeks in the role.
The BBC has been told she is stepping down due to “an honest mistake” rather than a disagreement over policy.
It is understood the PM was advised that the ministerial code had been breached.
Ms Braverman is the second cabinet minister to leave government during Liz Truss’s premiership.
Her departure adds further chaos to the week for the prime minister, at a time when Downing Street was desperate to show unity and stability in government.
Her replacement, however, could be another opportunity for Ms Truss to try and bring in someone who is not a natural political ally to shore up her support.
Ms Braverman becomes the shortest serving home secretary since World War Two, having been in the job for only 43 days.
Responding to her resignation, Labour’s shadow home secretary Yvette Cooper said the government was “falling apart adding: “To appoint and then sack both your home secretary and chancellor within six weeks is utter chaos.”
The Liberal Democrats Alistair Carmichael said: “The only solution now is a General Election so the public can get off this carousel of Conservative chaos.”