Anyone identify this fruit?

Trifoliate orange

It's a trifoliata orange, which is often used as the rootstock to graft other citrus onto because it can survive colder climates. https://en.m.wikipedia.org/wiki/Trifoliate_orange

It's in Australia.

Could be anything. However bergamot popped into mind first. But could just be an unripe orange

I thought kaffir lime at first but it's likely an unripe trifoliate orange