Hmm hmm that's nice. You might find it's not a Mandaville at all, but a Beumontia grandiflora. I planted one as well and it took forever to flower. One day it suddenly took off up a tree with no warning. From the very top of a sizeable guava tree it burst into a lovely shower of great big white angelic bells. Then a porcupine chewed it's thick corky base and that was that. After all those years.
Enjoy, has it got a smell, I never climbed up to smell?