Singapore Prime Minister Lee Kuan Yew made a landmark speech against Malay political dominance in the Malaysian Parliament in Kuala Lumpur in May 1965 which so angered Umno leaders that many felt Singapore had to leave.
Then Malaysian Prime Minister Tunku Abdul Rahman later called the speech the straw that broke the camel's back, while Singapore's former Cabinet minister Lim Kim San called it the speech that changed history.
"I had not expected my speech to play so crucial a part in the Tunku's decision to get Singapore out of Malaysia," Mr Lee wrote in his memoirs.
Before the fateful speech, tension between Mr Lee's People's Action Party (PAP) and Malaysia's ruling Alliance coalition headed by Umno had already been escalating. Mr Lee was making a good impression on the international media.
The PAP had formed the Malaysian Solidarity Convention (MSC), an opposition alliance whose members included parties from Sabah and Sarawak. This did not sit well with some Umno members.
As Mr Lee noted in his memoirs, he made his most important speech in the federal Parliament to "a hostile and tense audience, including a large number of Malay MPs fed daily with anti-PAP, anti-Lee Kuan Yew and anti-Chinese propaganda".
Mr Lee expressed regret that the King's Address at the opening of Parliament "did not reassure the nation that it would continue to progress in accordance with its democratic Constitution towards a Malaysian Malaysia".