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 delivered by his solicitor Darragh Mackin and close friend Jim McIlmurray - who has worked closely on the Hooded Men case.
Mr McIlmurray said Mr Clarke didn't believe the apology would come before his death but hoped other members of the group would receive one.
Mr McIlmurray explained that as Mr Clarke's health failed in recent weeks "negotiations intensified".
He said that after he received the letter of apology he and Mr Mackin brought it to Mr Clarke's bedside.
"I had the privilege of reading it to him in the presence of his wife," Mr McIlmurray said.
"Joe responded saying "Ah brilliant, brilliant" this was actually the last words he spoke."
Mr McIlmurray described the encounter as "emotional".
"I held his hand and said 'well, we done it'," he said.
"He knows he got the apology."
Mr McIlmurray said he was unable to tell anyone what had taken place at Mr Clarke's home.
"I was sworn to secrecy since last week and I could not even tell the Hooded Men what I did, or tell them what the content was of the meeting they were to attend today," he said.
Mr Mackin, of Phoenix Law, said the apology "brought Joe and his family great closure".
"He made it clear he found the apology 'brilliant, brilliant' and he tapped it twice, went back to sleep," he said.
"For all of these men (Hooded Men) I know it brings them even more comfort to know that Joe Clarke has gone but had some element of closure before he sadly passed away."
Mr Mackin was involved in negotiating the apology with the PSNI over the past 18 months.
It recognises the ill treatment the men were subjected to more than half a century ago.
It 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."
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.
One of the group, Kevin Hannaway said he does not accept the apology.
"We are not finished, we are going to take it as far as we can take it," he said.
"Why will the British government not admit to it?"
Mary McKenna, whose father Sean died in 1975, welcomed the development.
"As a family we welcome this apology from the PSNI," she said.
"We have been fighting for the truth about what happened to my father for 50 years and now the British government and military need to apologise for the torture of the hooded men."
Tony Shivers, whose father Pat died in 1985, said it was a "momentous day but tinged with sadness for Joe".
"We are delighted after 52 years because we knew what happened," he said.
Ms McKenna's solicitor Gemma McKeown, of the Committee on the Administration of Justice, described the development as "significant".
"The onus is now on the British government and MoD to acknowledge their role," she said..
"As the PSNI told us, this is the right thing to do."
Mr Mackin said the men have "fought a 10 year campaign for justice".
"This is a seismic development in a seismic case," he said.
"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."
He also 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."
The PSNI "expressed sympathy" to the family of Joe Clarke.
Detective Chief Superintendent Ian Saunders, Head of Legacy Investigation and Disclosure Branch said police have written Mr Clarke and relatives of the dead.
“The Police Service recognise the significant step taken today in issuing this apology," he said.
"It is our view that this was the right thing to do to help give the ‘Hooded Men’ and their families recognition about how they were treated.”
A UK Government spokesperson said: "We acknowledge the pain and suffering felt by so many during the Troubles.
"There are several ongoing legal proceedings in relation to this incident, and therefore it would be inappropriate to comment further at this stage.
The MoD issued an identically worded statement.
"We acknowledge the pain and suffering felt by so many during the Troubles.
"There are several ongoing legal proceedings in relation to this incident, and therefore it would be inappropriate to comment further at this stage."
