Canadian Prime Minister Stephen Harper's top aide has resigned over his role in a growing expenses scandal.
Nigel Wright quit after revelations he had given a senator 90,000 Canadian dollars (£58,000; $87,000) to repay improperly claimed housing expenses.
The conservative prime minister said he had accepted the resignation of his chief of staff "with great regret".
Mr Wright is now expected to be replaced by Ray Novak, media reports in Canada say.
Sen Mike Duffy, a former journalist, resigned from the Conservative caucus on Thursday two days after revelations about the cheque emerged.
Nigel Wright is a managing director of a major Canadian private equity firm who has been on secondment to the prime minister's office since 2011.
Opposition lawmakers say his cheque broke ethics rules barring senators from taking presents.
On Sunday, Mr Wright said in a statement that he had decided to step down "in light of the controversy surrounding my handling of matters involving Senator Duffy".
He stressed that he had not informed the prime minister about the cheque.
The federal ethics commissioner is now examining the matter.
On Friday, Senator Pamela Wallin also resigned from the Conservative caucus over an audit into her travel expenses.
She is among four senators whose expenses have been under scrutiny since December of last year.
The Senate's internal economy committee demanded hefty sums be repaid by Sen Duffy, Liberal Senator Mac Harb and Conservative Senator Patrick Brazeau, who is on a leave of absence over a separate matter - a criminal complaint of assault and sexual assault.
Canadian senators are appointed on the advice of the prime minister and may serve in the Senate until age 75.
The prime minister thanked his chief of staff for his work since 2011, accepting that he believed he had acted in the public interest.
Ray Novak, who is reportedly replacing Nigel Wright, has acted as Mr Harper's principal secretary for several years.