This pair was photographed in Khao Yai, e. Thailand in April.
The extensive blue on the forewing, the general colouration, and the curved discal line on the forewing lead me to believe that this should be T. isaeus. And it matches images on the web.

Subspecies verna is known from several locations in southern Thailand, and subspecies tyro is listed historically for northern/eastern Thailand (though no recent records, and is not listed for Thailand by Yutaka).

Confirmation or correction of the ID appreciated please. With thanks.