Lesotho's 80-year-old Prime Minister Thomas Thabane has told AFP news agency that he "intends to resign on Wednesday because of old age".
He is accused of murdering his estranged wife, allegations that caused his coalition government to crumble on Monday, leaving him without enough seats to continue governing.
The parliamentary speaker consequently announced that he had to step down by 22 May.
Mr Thabane and his current wife Maesaiah deny involvement in the murder of Dipolelo Thabane - who was shot several times outside her home in 2017, on the eve of Mr Thabane’s inauguration.
Dipolelo’s murder case is still before the courts.
The prime minister, whose term ends in 2022, is quoted by AFP as saying in a telephone interview on Tuesday that he is keen on ensuring his retirement is "as smooth as possible".
He said he would inform the king of the tiny mountain kingdom of his decision.
"I will have to go and inform him that I am leaving. Normally he would say 'fine'," he was quoted as saying.
Many in Lesotho believe that Mr Thabane has spent the last few months trying to lobby those in power for immunity from prosecution.
His party, the All Basotho Convention (ABC), has previously said he will not be receiving any protection from the law.