It also includes rare oral history from Mr Lee's wife, Madam Kwa Geok Choo.
Malaysia's Prime Minister Tunku Abdul Rahman had decided at this point that Singapore had to leave Malaysia.
He wrote to then-deputy prime minister Tun Razak of his thoughts about removing Singapore from Malaysia.
"Ultimately, I fear we will have no choice but to cut out Singapore from Malaysia in order to save the rest of the body from gangrene."
It was a thought that would turn into reality.
The merger between Malaysia and Singapore just two years back in 1963 would disintegrate a month later.
And not everyone wanted to see Malaysia split and Singapore - with its British bases - left on its own to survive. Even Mr Lee Kuan Yew had his own reservations about separation, hoping for a looser federation instead.
But despite the Tunku's decision - with the People's Action Party's (PAP) Dr Goh Keng Swee also proposing a separation - Singapore becoming an independent country would not have happened without the deepest secrecy.
Here's what truly happened in the 40 days leading up to Separation as told by key characters, including Madam Kwa Geok Choo - the wife of Mr Lee, whose supporting role in the separation is not always spoken about.
It had not been smooth-sailing since the formation of Malaysia, which saw the inclusion of Singapore, Sabah and Sarawak to Malaya in 1963.
Communal riots, race-based tensions, inflammatory political comments, and the seemingly growing allure of the PAP in the mainland led to much tension between the Tunku-led Alliance Party and PAP.
The rhetoric against PAP's Lee had also been ratcheting up.
Amid these developments, PAP's Mr Toh Chin Chye and Mr S Rajaratnam had been integral in getting the Malaysian Solidarity Convention (MSC) off the ground.
The MSC was a gathering of five political parties, namely PAP, the United Democratic Party and the People's Progressive Party from Peninsula Malaysia, and Sarawak's Machinda Party and the Sarawak United People's Party.
They had come together on May 9, 1965, in an attempt to staunch the spread of communalism in Malaysia.
All these developments alarmed the Malaysian leadership, particularly the Tunku, leading to his letter to Tun Razak on Jul 1.
A series of negotiations between Dr Goh and Tun Razak in the following days followed, crystallising thoughts and setting things in motion that would see Singapore finally split from its Causeway neighbour.
Dr Goh was, in fact, done with the idea of making Malaysia work.
Hear it in his own words:
Mr Lee soon bought into the idea, and subsequently instructed Law Minister Eddie Barker to draft the amendment to the constitution making the secession of Singapore possible, and an Act giving Singapore independence under that amendment.
Mr Lee also got Mr Barker to draft a proclamation of independence.
But he wasn't satisfied with the drafts shown, which was when he enlisted his wife - a "good conveyancing lawyer" - for her views.
Crucial to independence was securing Singapore's water supply from the Johor government.
On Mdm Kwa's end, she applied her draughtsman's lenses on the documents.
Her "duty"? Identifying areas of "ambiguities which can later lead to disagreement and conflict".
History has shown that her contributions in this regard have been invaluable.
After the flurry of activities to get the documents in order, a seeming lull descended by the end of July.
Mr Lee said in his memoirs that on Jul 30, he was "still uncertain as to what would happen, whether there would be a rearrangement, a separation, or a collision".
He added that he left Singapore to attend a PAP rally in Kuala Lumpur (KL) before going on to Cameron Highlands for their annual family holiday from Aug 2 to Aug 8.
It was here that Mdm Kwa played a small, but significant, role in allowing Mr Lee to slip into KL midway through their holiday to determine the next course of actions that would alter the histories of Singapore and Malaysia.
"I knew that things were coming to the boil ... meaning that the separation was going to take place," Mdm Kwa recounted in her oral history.
With that in mind, she managed the children and fobbed off any queries about Mr Lee's presence by saying he was at the golf course.
Whoever might have been sniffing around was none the wiser.
It was crucial to keep up the pretense as the British might have scuppered the act to separate had they caught wind of the plans.
Mr Lee said as much in his memoirs: "I was apprehensive that (Antony Head, the British High Commissioner then) might have got a whiff of what was going on."
"I knew that if he had the slightest hint of it, he was resourceful and strong enough to unscramble whatever we had agreed upon," Mr Lee wrote.
Things fell into place.
The secrecy gave Mr Lee and his leaders the cover and time needed for the Separation documents to be finally signed off on both sides.
At the end, Mr Lee thanked Mr Barker and said: "We've pulled off a bloodless coup."
But for Mr Lee and all the other Malaysian leaders in the know, the day would be history making - for both countries.
And the impending moment was to keep him up at night.
"Spent a fitful night tossing and turning because it was very upsetting, we were letting down so many people," Mr Lee recounted.
The morning heralded a new dawn for peoples in both countries; the proclamation of independence was broadcast on radio in Singapore at 10am.
It was the press conference that took place after that would prove most memorable.
As Mr Lee fronted the cameras to explain the decision and rally Singaporeans to their new reality, he had to face up to ending the dream of a united Malaysia.
But the lack of sleep, the emotions of the press conference and all the details he had to oversee prior to Separation had taken its toll.
Mdm Kwa said he was "very, very upset" after he returned in the afternoon.
"That is the nearest I have seen him to being near a nervous breakdown."
The whirlwind romance between Malaysia and Singapore was over.
Yet the ramifications of the decision are felt to this day.
You can dive into all the declassified documents released as part of Dr Goh's Albatross File, and the newly released oral histories from key figures during this period.
Check out The Albatross File: Singapore's Independence Declassified exhibition at the National Library Building that opened on Dec 8, 2025.