. Looks like a gorgeous shrub.
There's only a thumbnail picture in my RHS A - Z Encyclopedia of Garden Plants, (1998 edn. ISBN 0-7513-0303-8) but on page 522 it looks as if it could be Hibiscus Syriacus
Found this [url=https://www.ces.ncsu.edu/depts/hort/consumer/factsheets/shrubs/cultivars/hibiscus_syri-redheart.html]online picture here.[/url] The stamens are different looking but you may have captured a more mature flower about ready to drop petals.