Sunanda Kumariratana (Thai: สุนันทากุมารีรัตน์; rtgs: Sunantha Kumarirat, 10 November 1860 – 31 May 1880) was a queen consort of Siam. She was a daughter of Siamese King Mongkut (Rama IV) and Princess Consort Piam. She was the half-sister and first wife of King Chulalongkorn (Rama V) of Siam (now Thailand). The kings's other two wives were her full-sibling younger sisters, Queen Savang Vadhana and Queen Saovabha Bhongsi.

The queen and her daughter drowned when her royal boat capsized on the way to the Bang Pa-In Royal Palace (Summer Palace). The many witnesses to the accident did not dare to touch the queen, a capital offense—not even to save her life. The grief-stricken Chulalongkorn later erected a memorial to her and their unborn child at Bang Pa-In Palace.

...
Wikipedia