The disgraced former leader of the Democratic Unionist Party is being investigated by the Metropolitan Police over an alleged rape inside the Houses of Parliament.
She has been interviewed by the Police Service of Northern Ireland who have shared her allegations with officers in London, the BBC first reported.
The ex-MP was last week sentenced to 15 years for a series of child sex offences against two victims.
They included one count of rape, which took place between 1985 and 2008.
His solicitor has previously confirmed that papers have been lodged for an appeal.
Jeffrey Donaldson is a former MP
PA Wire
The Met has issued a statement confirming a 63-year-old man is being investigated but did not name Donaldson directly.
A force spokesman said: "On Tuesday October, 13 the Met received a report referred to us by the Police Service of Northern Ireland relating to an allegation of rape in 2016, by a man now aged 63.
"The allegation relates to one victim who is being supported by specialist officers.
"The investigation is in its early stages. No arrests have been made and enquiries are ongoing."
The Belfast Telegraph reported in July that a woman from Northern Ireland had made allegations that she was sexually assaulted by Donaldson in the DUP offices in Parliament in 2016.
He attempted to get her to drink shots of vodka before attempting to kiss her and put his hand up her skirt, she claimed.
The newspaper on Saturday reported that the Met was set to investigate and interview the former DUP leader about these accusations.
It has now emerged the same woman has also alleged she was raped.
Donaldson was jailed last week for 11 years for rape against one victim and a further four years for assaults on a second victim, to be served consecutively.
During sentencing, Judge Paul Ramsey said the former politician had experienced a “catastrophic descent into disgrace”.
“There has not been, and doubtless will not be, one word of regret, apology or shame from this man to at least provide his victims with some crumb of comfort,” he said.
The DUP said Donaldson “deserves every day of the lengthy prison service he has to serve”.
In a statement, the party added: “Justice has been done with the sentencing of Jeffrey Donaldson for his vile and disgusting crimes against his victims.
“Our first thoughts are again with the innocent victims, who having suffered such evil, were re-traumatised through giving evidence at the trial.
“They deserve our compassion, support and respect. We hope they can find some measure of comfort and can look ahead to a new chapter in their lives.”