Prime Minister Lee Hsien Loong said the buildinghas a significant place in Singapore's history and holds special meaning to the country and its people.
"This transformation of the building, in a way, is a reflection of how Singapore as a nation transformed in one lifetime, going from an old historic building something which has been updated, keeping the essence of the old, but of this age and up-to-date and better than before," Lee said.
The 1928-built grand Neoclassical building declared as Singapore's 71st National Monument, is situated at the mouth of the Singapore River.
The 400-room pentagon-shape Fullerton Hotel is rated among the best in the world.
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Before that it wasSingapore's General Post Office and housed several government departments, where some of Singapore's pioneer leaders began their careers.
Lee said the occasion was made "all the more special" because it happened during Singapore's Jubilee Year or 50 years of independence celebration.
The building is one of the most iconic colonial buildings in Singapore, standing at the mouth of the Singapore River and defining the Singapore skyline since the 1920s.
The buildingalso had a roof-top lighthouse from 1958 to 1978, guiding ships 30 miles away to Singapore harbour.
Named after Sir Robert Fullerton, the first Governor of the Straits Settlement (1826-1830), the Neoclassical building then cost SGD 4.75 million to construct.