Most likely male Caltoris bromus.

There is a relatively large upper cellspot present, indicating there will be two cellspot.

C. malaya have no cellspot ; Occasionally only tiny ones.
http://yutaka.it-n.jp/hes/93360001.html


C. cormasa usually have only a lower cellspot; if the upper cellspot is present, it is tiny.
Undersde HW a darker reddish brown.
https://1.bp.blogspot.com/-8EbM65dWq...C_adult_03.jpg
http://yutaka.it-n.jp/hes/93340001.html

Two similar spwxiws with two cellspot in Singapore are C. bromus & cahira.

C. cahira; HW very dark chocolate brown.
P. Malaysia male.
https://www.flickr.com/photos/gancw1/21680122591
Female Singapore.
http://4.bp.blogspot.com/-7l1dr3n_gK...ris+bromus.jpg


C. bromus HW dark brown with an ochreous overlay.
The female is the only species here where two white spots in space 2 & 3 may be present.

Female Singapore.
Upperside with two cellspot.
https://inaturalist-open-data.s3.ama...peg?1626102276
Underside with HW white spots 2 & 3.
https://inaturalist-open-data.s3.ama...peg?1626102279

Male is without is always without the HW spots.
http://yutaka.it-n.jp/hes/93320001.html
Taiwan male.
https://data.taieol.tw/files/eoldata...9/00126473.jpg
Another Singapore male.
https://inaturalist-open-data.s3.ama...peg?1626603050


TL Seow: Cheers.