I spotted it again at Pulau Semakau. And this time, the identity of that bird has been established. It happened that there's some nature society people over at that island, snapping photos of the nature, when the bird start soaring, and suddenly, all the cameras, mine included started aiming and snapping away at that majestic bird.
It's known as the Brahminy Kite. Scientific name, Haliastur Indus
My photos of that bird.
Here's the URL for you to visit.