Hooded Man Joe Clarke received a death bed apology from the PSNI over his treatment after he was interned more than 50 years ago.
He was one of 14 Catholic men who say they were subjected to state-sanctioned torture when they were held without charge in 1971.
The surviving members of the group also received an apology on Tuesday morning.
Mr Clarke (71) died at his home in south Belfast on Monday afternoon.
None of the Hooded Men were convicted of any wrongdoing.
It has now emerged that Mr Clarke received an apology from the PSNI last Thursday, which was deliver by his solicitor Darragh Mackin and close friend Jim McIlmurray - who has worked closely on the Hooded Men case.
The remaining members of the group also received an apology during a meeting with senior PSNI figures at Garnerville in east Belfast on Tuesday morning.
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The techniques used against the 14 men included being hooded, made to stand in stress positions, forced to listen to loud static noise and being deprived of sleep, food and water.
In 2021, the Supreme Court ruled that the methods used "would be characterised today" as torture.
The PSNI apology recognised the ill treatment the men were subjected to.
The apology said: "The Police Service of Northern Ireland acknowledges the finding of the United Kingdom Supreme Court that it is likely that the treatment to which you and the other Hooded Men were subjected to at the hands of the security forces, including some police officers, would be characterised today as torture.
"We wish to acknowledge that the treatment you received was not acceptable at that time and is not acceptable by modern standards of policing.
"We would like to convey an apology to you for the actions and omissions of police officers at that time."
Mr Mackin, of Phoenix Law, was involved in negotiating the apology with the PSNI over the past 18 months.
“The Hooded Men have fought a 10 year campaign for justice," he said.
"Since their landmark victory before the Supreme Court in December 2021, we have engaged at the very highest level to try and find a resolution for our clients.
"Today, almost 18 months on, the PSNI have today issued our clients with a formal apology that recognises the torturous treatment to which our clients sustained. "
Mr Mackin said the publication of the apology comes after "after weeks of intense negotiation" which drew to a close in the days before Mr Clarke died.
"In the last days of his life, Mr Clarke was finally delivered closure in the form of an apology, for which he had long since campaigned," he said.
"This is a seismic development in a seismic case.
"Most importantly, in times of debate on how the legacy of the past should be addressed, we can and should forever point to the case of the Hooded Men as the pin up of due process, humanity and resolution coming together under one umbrella. This case is an example of why the efforts by the British government to brush the legacy of the past under the carpet will never, and can never, work."
Mr Mackin also paid acknowledged the role of the PSNI.
"Tribute ought to be paid to those at the upper echelons of the PSNI and in particular ACC (Alan) Todd and their legal advisor Mr Ian Saunders who despite the sensitivities engaged in an extensive negotiation, and against all odds, ensured the delivery of an apology before the passing of Mr Clarke.
"Today, those efforts must be acknowledged and appreciated in what is truly a landmark development.
"Mr Clarke was a larger than life character who had unrivalled generosity and charisma. This apology is a testament to that character and tenacity, in demonstrating that where there is a will; there is always a way.”
It is understood some members of the group received their apology during a meeting with senior PSNI officers at Garnerville in east Belfast.