Sir Jeffrey Donaldson MP has been charged with rape and other historical sexual offences and has resigned as Democratic Unionist Party (DUP) leader.
A 57-year-old woman has also been charged with aiding and abetting in connection with the alleged offences.
They were both arrested on Thursday morning by PSNI detectives and were questioned before being charged on Thursday night.
Sir Jeffrey had said that he will be strenuously contesting the charges.
He and the 57-year-old woman are due to appear in court next month.
In a statement the DUP said: “The party chairman has received a letter from Sir Jeffrey Donaldson MP confirming that he has been charged with allegations of an historical nature and indicating that he is stepping down as leader of the Democratic Unionist Party with immediate effect.
“In accordance with the party rules, the party officers have suspended Mr Donaldson from membership, pending the outcome of a judicial process.
“The Party Officers have this morning unanimously appointed Mr Gavin Robinson MP as the interim party leader.”
Sir Jeffrey’s letter to the DUP states he will be strenuously contesting the charges.
DUP interim leader Gavin Robinson said it has been a “devastating revelation”.
“It has caused a tremendous shock, not just for myself personally, or my colleagues within the DUP, but for the community right across Northern Ireland,” he said.
“We are a party and individuals that believe in justice, we have faith in our criminal justice system and so in the coming days and months, we think it is important that none of us say anything or act in any way that would seek to prejudice what is now an ongoing criminal investigation.”
He added that it was “very late last night” when the party first became aware of the allegations.
Mr Robinson said the most important task for the party is “focusing on the importance of making Northern Ireland work, instilling a sense of positivity in devolution and making sure that devolution works for our people.”
What happened on Friday?
Police issued a statement on Friday morning, but did not disclose the identity of those charged.
The statement said a 61-year-old man had been charged with “non-recent sexual offences” adding that a 57-year-old woman was also arrested at the same time and charged with “aiding and abetting additional offences”.
The statement also confirmed the pair would appear before Newry Magistrates’ Court on 24 April.
The police investigation is understood to have started within the last number of months, after two women came forward.
It is understood DUP officers met on Friday morning after details of the charges emerged.
Sir Jeffrey’s social media accounts, including on X, were deleted overnight.
Analysis box by Enda McClafferty, NI political editor
This is a political bombshell like no other in Northern Ireland.
Sir Jeffrey Donaldson was at the peak of his powers. He steered his party back into Stormont in the face of opposition of many of his own MPs and peers.
But now his political career appears to be over and his party has been left in disarray.
Gavin Robinson has now stepped up and will attempt to steady the party which has been rocked by the allegations facing its former leader.
Mindful of the potential risks to Stormont, Sinn Féin First Minister Michelle O’Neill warned that the Executive must continue to deliver for the whole community.
A coded warning to the DUP to look beyond its own internal challenges and keep the bigger political prize in view.
Sir Jeffrey Donaldson was elected leader of the DUP in 2021.
He is also the longest serving MP in Northern Ireland having been first elected to Parliament in 1997.
Sir Jeffrey recently steered his party back in to government in Northern Ireland ending a two year boycott of the Stormont institutions.
The DUP had walked out of government in protest at the Northern Ireland Protocol, claiming the post-Brexit arrangements had undermined their place in the UK.
Sir Jeffrey was first elected to parliament in 1997 as a representative of the Ulster Unionist Party (UUP).
In 2003, following long-standing opposition to the Good Friday Agreement and the leadership of David Trimble, he announced he would leave the UUP, later joining the DUP.
He was awarded a knighthood in 2016 for political service.
Source: BBC