My first thought was Lycoris, but they're fall bloomers. The only other thing I can think of is Rhodophiala, and that's also not a Spring bloomer.

Suja

I did a search and the flower that comes up is a Belladonna lily (Naked Lady). That looks like the flower I'm talking about. Is this a spring or summer flower?

Late summer/early fall bloomer, I believe. Pretty much everything in the Amaryllis family tend to bloom towards the end of the season.

Suja

But the leaves come up in the spring, then die back, so when the flower comes up in August/September, it's "naked".

The foliage comes up in the early spring and dies back before the blooms appear in the summer. I actually had another flush of blooms from my Naked Ladies in the late fall. I don't know if these were repeat bloomers or plants that hadn't flowered in the summer.