VETERAN MP Ong Chit Chung died at his home early on Monday morning. He was 59.
The cause of death has not been confirmed.
Dr Ong, a lecturer in military history at the National University of Singapore when he entered politics in 1988, was an MP for Jurong GRC.
MPs and grassroots leaders contacted earlier on Monday were shocked to learn of his death. One recalled that Dr Ong had just played golf on Sunday and looked active and well.
Upon hearing the news of Dr Ong's death, Foreign Affairs Minister George Yeo expressed regret and offered his condolences to Dr Ong's family.
Mr Yeo said: 'Over the years, Chit Chung took a close interest in foreign affairs and was always helpful to diplomats and ministry officials'.
'At a personal level, I knew him from SAF days when he lectured Military History. We entered politics together twenty years ago in 1988, never expecting when we did that we would be serving so many years. I treasured his friendship and his advice as a friend and a colleague', he added.
Senior Minister of State for Foreign Affairs Zainul Abidin Rasheed said that he would miss Dr Ong, remembering him as a 'close friend that cares, inside and outside Parliament'.
Mr Zainul also described Dr Ong as 'one of the Senior MPs who showed tremendous friendship and care', helping him to 'settle in as an MP and as Senior Parliamentary Secretary' when he 'was first appointed to MFA', reminding him 'to try achieve a good balance between work, the ground and family'.
Mr Michael Pek, senior constituency manager at the GRC's Bukit Batok ward and who has known Dr Ong for 14 years, described him as a conscientious leader who knew his grassroots leaders well and cared for his residents.
He said that Dr Ong had, for instance, ensured that bursaries were given out to some 200 to 300 students from low-income families in his ward who did not qualify for Edusave bursaries.
During his twenty years in politics, Dr Ong served two terms as MP for Bukit Batok from 1988-1996; one term as MP for Bukit Timah GRC from 1996-2001; and was into the middle of his second term as MP for Jurong GRC 2001-2008 when he died.
From 1991 to 1993, Dr Ong was also the Parliamentary Secretary for the Ministry of Home Affairs and the Ministry of Labour.
Dr Ong leaves behind a wife and two sons.