The female of the Malay Viscount (Tanaecia pelea) is often confused with the Malay Baron (Euthalia monina), 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 rounded forewing tip, I think it is the Malay Viscount but I am not 100% sure.
Sungei Buloh Wetland Reserve, Singapore, 25 October 2022