Necklace which can be converted into a diadem, with old

Necklace which can be converted into a diadem, with old cut diamonds of approx. 18.78 ct in total. 19th century.
Features twenty-one floral motifs in decreasing size with inlaid central brilliant of approx. 8.82 ct in total, petals with rose cut diamonds of approx. 2.52 ct in total and twenty-one alternating old cut brilliants of approx. 4.62 ct in total.
Central detachable pendant in flower design with old cut brilliant of approx. 0.83 ct and petals set with rose cut diamonds (one missing) and old brilliant, with total weight approx. 1.99 ct.
Yellow gold mounting 18K backed with silver.