As Margaret Thatchers Principal Private Secretary, Robin Butler was at the beck and call of a prime minister who seemed to relish working late into the night.
But in the small hours of October 12, 1984, the night before the second to last day of the Tory Party conference, the civil servant was surprised when Mrs Thatcher looked as though she was going to head off to bed early - shortly after 2.30am.
But Lord Butler, as he now is, had a final bit of paperwork for the PM to look at in her suite in Brightons Grand Hotel, and so she stayed up a bit longer.
Moments later, the bomb that had been made and planted by IRA terrorist Patrick Magee in room 629 on the sixth floor a month earlier exploded.
Mrs Thatchers bathroom, which she had been in just minutes earlier, was severely damaged. She escaped death or serious injury by a whisker.
Speaking to MailOnline, Lord Butler, now 86, recalled: What I remember is thinking, "God, thats a bomb, I better do something sensible".
That sensible thing was to tell Mrs Thatcher to come away from the windows, in case there was another explosion.
Remarkably, the lights had not gone out, despite the enormous damage wrought by the blast.
Margaret Thatcher seen alongside her husband Denis and personal assistant Cynthia Crawford as she leaves Brightons Grand Hotel shortly after an IRA bomb attack, October 12, 1984
On October 12, 1984, a bomb planted by IRA terrorist Patrick Magee exploded. The aim was to kill Margaret Thatcher following her refusal to back down in the face of hunger strikes
The bomb had engulfed one of the two 11ft chimney stacks that stood atop the historic hotel.
The stack then careered through the hole created by the blast, ripping through several rooms.
Five people, including deputy chief whip Sir Anthony Berry and the wife of chief whip John Wakeham, were killed.
A further 31, among them trade and industry secretary Norman Tebbit and his wife Margaret, were seriously injured.
Amid the sounds of falling masonry, Mrs Thatcher ventured into the darkness of her bedroom to see if her husband Denis, who had gone to bed earlier, was ok.
I am left thinking, God, how am I going to explain to the tribunal that I let her go in while I waited outside, Lord Butler said.
She emerges leading Denis who is pulling trousers over his pyjamas.
The trio then went out into the corridor, where they saw Geoffrey Howe - then the foreign secretary - blinking slightly as he emerged from his own room.
Lord Butler, who went on to serve as Cabinet Secretary under Mrs Thatcher, John Major and briefly Tony Blair before retiring in 1998, said the emergency response to the blast was very quick and impressive.
The group were led out of the ruined hotel by a fireman, and then taken to spend the night at a police training centre in nearby Lewes.
Mrs Thatchers suite escaped largely unscathed, besides the bathroom, which was severely damaged. Had she been in there getting ready for bed, she could have been killed
Tonight, Lord Butler appears in BBC documentary Bombing Brighton: The Plot to Kill Thatcher. The programme airs at 9pm on BBC Two
Sir Robin Butler seen cycling along the Embankment in London in 1987. He became Cabinet Secretary in 1988 and served in the role for a decade
How the bomb planted by Patrick Magee devastated the Grand Hotel in Brighton on October 12, 1984
Just hours after the attack, Mrs Thatcher appeared at the Tory party conference. She told the party faithful: ...The fact that we are gathered here now, shocked but composed and determined, is a sign not only that this attack has failed, but that all attempts to destroy democracy by terrorism will fail
The scene outside the Grand Hotel in Brighton, after a bomb attack by the IRA
Injured guests leave the Grand Hotel in Brighton, after a bomb attack by the IRA
A policeman stands over a man who has been injured in the bomb blast at the Grand Hotel
Injured guests leave the Grand Hotel in Brighton, after a bomb attack by the IRA
A policeman in protective clothing searches for clues at the ruined Grand Hotel
The severe damage to a large section of the Grand Hotel, caused by a bomb blast which toppled a chimney stack
Police search through the rubble of the damaged part of the Grand Hotel after the bombing
That was after Lord Butler had foolishly gone back inside the structurally unsafe hotel to collect the PMs clothes and official papers from her room.
In Lewes, aides had put aside a room for the PM, her assistant Cynthia Crawford and Lord Butler, but not Mr Thatcher.
So Lord Butler generously gave him his room and tried to get some sleep in the centres day room.
News then came in of the extent of the casualties back at the hotel.
Lord Butler watched on TV as rescuers pulled a battered but conscious Lord Tebbit out of the rubble.
Mrs Thatcher then left her room. Lord Butler said: Margaret Thatcher emerges, wearing some of the clothes Id rescued.
I say to her, "Its much worse than we thought when we left the hotel."
And she says without batting an eyelid, "Well, the conference is due to start at 9:30 and we must make sure it starts on time."
And I am horrified, I said, "Youre not going to go on with this party political event when some of your closest colleagues have been killed and others injured?"
And she said, in words Ive never forgotten: "This is our opportunity to show that terrorism cant defeat democracy."
In June 1985, what had turned into an international manhunt for Patrick Magee came to an end. He was arrested and handed eight life sentences after a trial
Magee seen being released from prison in 1999. He was let free after 13 years under the terms of the Good Friday Agreement
Patrick Magee features in tonights BBC documentary Bombing Brighton
Mrs Thatcher went on to get a standing ovation lasting several minutes after telling the party faithful: ...The fact that we are gathered here now, shocked but composed and determined, is a sign not only that this attack has failed, but that all attempts to destroy democracy by terrorism will fail.
Having watched the performance, Lord Butler conceded that it was the right thing not to cancel the conference.
I have always said that she was right and I was wrong, he said.
Tonight, Lord Butler appears in BBC documentary Bombing Brighton: The Plot to Kill Thatcher. The programme airs at 9pm on BBC Two.
Also featured is Jo Berry and her brother Edward, the children of bomb victim Sir Anthony Berry.
Remarkably, she has forged a form of friendship with Magee - who himself speaks in the programme - after initially meeting him a year after his release from prison in 1999.
Ms Berry, a peace campaigner, has shared a platform with the former terrorist more than 300 times as part of her lifelong efforts to promote dialogue and conflict resolution.
She is the founder of the charity Building Bridges Through Peace.
Lord Butler said he is uncomfortable about Ms Berrys decision to associate with Magee.
He added: The only time I ever clapped eyes on him was when I went to an hour or two of the trial in the Old Bailey.
The striking thing about him is that he has remained an utterly professional and committed former member of the IRA.
He has never given any details of what they did or how they did it. He has remained a disciplined soldier, as he would see it.
At his trial, the judge described Magee as a man of exceptional cruelty and inhumanity.
The terrorist had stayed at the Grand almost exactly a month before the night of the explosion, under the pseudonym Roy Walsh.
Bizarrely, his choice was the name of a well-known IRA operative who was serving time in prison.
It remains a mystery as to why Magee chose a name that could have raised alarm bells before the Tory conference began.
He previously insisted that the choice was a random, spur of the moment one.
Magee planted a bomb under the bath in his room, number 629.
The device, which Magee - an experienced bomb maker - had built himself, was fitted with a long-delay timer.
When the bomb went off, the terrorist was back in Ireland. It was not long before he continued to plot further attacks.
In June 1985, what had turned into an international manhunt came to an end.
Scottish detectives stormed an apartment in Glasgow and arrested Magee with four other IRA members.
He had been tailed to Scotland after meeting fellow IRA man Peter Sherry in Carlyle.
Police who were watching the meeting identified Magee - by then a veteran IRA terrorist - because they knew that he had part of one of his fingers missing.
Magee was handed eight life sentences after his trial at the Old Bailey, with a recommendation that he serve a minimum of 35 years.
However, he was released 13 years later under the terms of the Good Friday Agreement.
The Daily Mails coverage the day after the blast, detailing how Margaret Thatcher had been in her bathroom just minutes before it was wrecked by the blast
The Daily Mails coverage of the 1984 bomb attack on the Grand Hotel in Brighton
The Daily Mails coverage. It reported how Marks & Spencer opened early in Brighton so conference attendees could buy new clothes
Lord Tebbit, 93, remains vociferously unforgiving towards Magee. His wife, who died in 2020, was left permanently disabled by the blast.
The former minister previously said: I am often asked if I can find it in my heart to forgive the creature, Patrick Magee. That is not possible, for Magee has never repented.
One can hope that theres a particularly hot corner of Hell reserved for him and he can repent in his own time there.
Lord Butler, who was also present when the IRA attacked Number 10 Downing Street with mortar fire in February 1991, was characteristically matter of fact as he concluded his recollection of the events of October 12, 1984.
He said: It was just a thing that happened. It was part of many IRA attacks, and of dealing with that phase of our history.
Bombing Brighton: The Plot to Kill Thatcher, airs tonight on BBC Two at 9pm.