It is a member of the Ornithoptera priamus species group which, including croesus, is only found east of the Wallace Line.

On taking it out of my net and opening the glorious wings, my heart began to beat violently, the blood rushed to my head, and I felt much more like fainting than I have done when in apprehension of immediate death.

There is a clearly visible long oval sex brand (of androconial scales) in the black area.

Female: typical of birdwing butterflies, Ornithoptera croesus is strongly sexually dimorphic.

[1] It is also listed in the Appendix II of CITES, restricting international trade to captive-raised specimens only.