The Malay Baron (Euthalia monina) is one of the commonest species of the genus Euthalia in Singapore. 
The species is unusual in that the male is polymorphic with at least 3 different forms found in Singapore.
The female of this species is often confused with the Malay Viscount (Tanaecia pelea), which also occurs in Singapore, but also with other very similar species within the Euthalia genus and Tanaecia genus.
One of the slight differences between the Malay Baron and the Malay Viscount is that the forewing apex is sharper in the Malay Baron while in Malay Viscount it is much rounder.
There are also slight differences in the shape and form of the arrowheads and zigzag line on the wings, but only an expert can spot these differences.

This is a female and looking at the rather sharp forewing tip, I think it is the Malay Baron but I am not 100% sure.

Pulau Ubin, Singapore, 24 October 2022