A REAL CENTURY PLANT, OR A FLOWERING SPANISH DAGGER?

By Juan Montoya
A friend of mine and I – neither of whom are botanists – have been trying to find what the name of this plant that suddenly sprouted a stalk and began to bloom in his back yard could be. It's going on 20 feet high and growing.
For years all that showed above the ground were the bright green (yellow?) spears bordered by a dark green. I've heard of the century plants that are supposed to grow this stalk every 100 years (or so the myth goes), but he insists it's just a blooming spanish dagger variety.
The "blooms," is they can be called blooms, are rather like aggregates of small bulbs with red pistils as far as we can tell from the ground. We're sure that there are others like it in someone else's yard who could tell us exactly what variety of plant this is. Does anyone know? And what happens after it blooms? Does it shrivel up or continue to grow?