It's a species of Asclepias (Milkweed). Host plant of the Monarch butterfly. Lucky you.

One of the Asclepias, aka Butterfly weed. They don't grow here , so I don't know the species.

BTW many weeds are perennials ;-)

Probably A. syriaca, common milkweed.

Thanks Everyone.

Seedmoney, it's not growing in my garden, but nearby. It sort of smells like Christmas in July. A bit disconcerting in the heat !

Floral, you're right :-)

However, if you saw the lot, covered with most vigorous weeds (perennial or not) of all sorts, seeing any flowering plant there is sort of miraculous.

Hortster, you're absolutely right. The flowers remind me of a pale ornamental allium. A perfect globe.