Tanzanian Diadem Butterfly Hypolimnas antevorta
The Tanzanian Diadem Butterfly, one of the Eggfly/Diadem family, as its name suggests, is native to Tanzania.
It looks somewhat like the Blue-banded Eggfly, but the blue band crosses the middle of the hindwings rather than following the outside edge.
Unlike the closely related Common and Danaid Eggflies, male and female have a similar appearance.
The underside is similar to that of the Common/Great Eggfly
Links:
Common Eggfly female