The head of Ofqual has quit in the wake of the A-level and GCSE results U-turn in England, the exams regulator said.
Sally Collier resigned as chief regulator after four years, just days before she was due to face questions from the Commons Education Select Committee over the exam results fiasco.
The Ofqual Board said it "supports" her decision that the next stage of the awarding process would be "better overseen by new leadership".
She will be replaced in the interim by her predecessor Dame Glenys Stacey, who will be acting chief regulator until December 2020.
Ofqual developed a standardisation algorithm for A-levels and GCSEs which resulted in hundreds of thousands of students having their results downgraded.
Those from more disadvantaged backgrounds were said to have been hit harder by the moderation system than private school pupils.
A u-turn was performed which allowed A-level students to use their predicted grades, which were higher, when applying to universities.
GCSE students were spared the stress of having downgraded results as the policy shift came before their grades were published.
Ministers had attempted to shift blame onto Ofqual over the results debacle.
Earlier Boris Johnson said with hindsight he "might have done some things differently" regarding the way results were standardised.
He said: "If we had to do it again, we might have done some things differently, I’m certainly not going to deny that.
“But they’ve got a series of results that they can certainly work with and use to develop their careers.”
The education secretary apologised to students following the u-turn but appeared to blame the algorithm on Ofqual, which he said had given him assurances it would be fair.
Following Ms Collier's resignation, Education Secretary Williamson thanked her for "the commitment she has shown to the role over the last four years".
He added: “I welcome Ofqual’s announcement that Dame Glenys Stacey is to assume a temporary leadership role as acting Chief Regulator and also the new internal governance arrangements put in place with Ofsted support.
"This will make sure Ofqual can fully focus on the important functions it must deliver as the independent regulator for qualifications, examinations and assessments in England.
“Moving forward, my department will continue to work closely with Ofqual’s leadership to deliver fair results and exams for young people.”