Sinn Fein has been left a £1.5 million donation in the will of a party supporter.
The money was given to the party by William E Hampton and was paid in two instalments of £1 million and £500,000 in April and May.
A source close to Sinn Fein told the PA news agency that Mr Hampton, who was born in London, died on January 11 2018 at his home in Pembrokeshire, Wales, at the age of 82.
Mr Hampton, who was not married and had no children, left some money to friends and acquaintances, but the main beneficiary of the will was the Irish republican party.
It is understood that he spent some time living in Ireland and was a long-time supporter of the party.
"He was not Irish, he was listed as British on his birth certificate, and his birthplace is listed as London," a party source said.
"He was a known supporter of Sinn Fein, and resided in Ireland at different periods.
"He made the will himself, and had it drawn up a few years ago, he's obviously been a supporter a long time and planned ahead."
It is understood that Mr Hampton had assets in other jurisdictions, which are still being litigated over, but the main assets were in England and Wales.
"The party have known about him for a long time and it wasn't exactly new information to the party as the will had been made a few years before," the party source added.
"The death, however, came out of the blue and was unexpected. The death certificate said he died of respiratory failure, and he was quite frail and elderly, so it was probably old age."
His career history lists Mr Hampton as a retired motor mechanic and driver.
The contribution is the largest donation given to a political party in Northern Ireland.
A Sinn Fein spokesman said: "Sinn Fein can confirm that it received a significant donation from a party supporter who passed away.
"We're obviously pleased that he has chosen to bequest this sum to the party and it's a positive boost to Sinn Fein in working towards Irish unity and towards our political objectives.
"We are in full compliance with the requirements of the Electoral Commission on all of this."
Other political parties in Northern Ireland received almost £338,000 in donations between April and June.
The Democratic Unionist Party (DUP) had previously held the record for the largest donation after a pro-Brexit group known as the Constitutional Research Council donated £435,000 in June 2016.
Legislation introduced in March allows donations and loans of more than £7,500 to parties in Northern Ireland to be made public, and covers donations from July 1 2017 onwards.