Can someone tell me what variety this could be? The plant blooms for the first time now and the flower isn't just double, it is quintuple and 5.5 inches across!!! The color is very deep red with darker eyes.

What I know about this plant is that the cutting was taken from an old hibiscus in a school or a bank or something which makes me think it might be some old european variant, perhaps even close to the kind that Linnaeus ID'd when Hibiscus first arrived to Europe from China.

Huge hibiscus