This butterfly appears to be seasonally common on Singapore Island, and up to a dozen or more can sometimes be found, frolicking in the same vicinity.  The species is dimorphic, where the male has broad black borders above, with a white bar edged with purple-blue.  The undersides are pale silvery grey with a purplish tinge.  There is a prominent ocellus near the tornus of the hindwing on the underside.
The female is brown with zig-zagged markings, and can sometimes be confused with the more common Malay Viscount (Tanaecia pelea pelea) when in flight. 
The species is the only representative of its genus in Malaysia and Singapore.  An interesting characteristic of this butterfly is that when disturbed or alarmed, it flies rapidly and zips to the underside of a nearby leaf where it settles with its wings closed.  Both the males and females exhibit the same behaviour.  The caterpillar host plant is the Gironerra species.

Butterflycirlce blog article - Life History of the Purple Duke