I thought that Avengers #17 had Ex Nihilo on the cover, but I've just realised that he's not.
This appears to be a female of his species. Note what looks like breasts, a different symbol on the chest, a different coloured eye, antlers rather than horns, etc.
Does anyone know who this is? There was no mention of her in this issue, and I don't recall any mention in the rest of the series.