Looks like the result of a serious impact. While the 21"s aren't the most robust in the first place, that's one of the worst bent examples I've seen. It looks like the rim is cracked from the picture. Is the lip pulling away from the wheel, which is why you've said it's separated? It's hard to tell from the image.
It's *maybe* repairable if bent, but given the severity I doubt it. If it's cracked or separated, it's time for a new wheel.