Hi folks, wanting to get a better idea of what this might be. It was sold as pomelo, would come from a few decades old tree (not imported fruit), Southern hemisphere. I don't have any photos of the tree sorry.
Zest: Smells just like grapefruit.
Extremely bitter, by far the bitterest Citrus part I've ever put in my mouth. Eating a small piece of zest numbs my whole mouth, with some tingling (no I'm not allergic to grapefruit or any other Citrus and eat plenty of Citrus rind, eat tons of marmalade etc)
Pith: Very bitter.
Flesh: Smells like some storebought lemonade drink with a grapefruit hint. Juice/flesh is fairly sour, bitter and not a lot of sweetness. I guess fairly similar to white grapefruit juice.
Seeds: Extremely large, rectangle shape.
Despite all this, I can't get rid of the idea of trying to make marmalade from the whole fruit... it would be immensely potent and probably just pure medicine taste. Madness.