Sisters Jeanette MacDonald and Marie Blake…
Marie Blake, also known as Blossom Rock (Rock being her married name), was born Edith Marie Blossom MacDonald on August 21, 1895 in Philadelphia to Daniel and Anne MacDonald. Marie was the elder sister of Jeanette MacDonald, who was born Jeanette Anna MacDonald in Philadelphia on June 18, 1903
According to Jeanette MacDonald biographer Sharon Rich (who was also close friends with Marie Blake), Jeanette was happy that her sister Marie finally gained widespread recognition playing Grandmama, and for that reason, Jeanette never missed watching an episode of The Addams Family.
–Annmarie Gatti for Classic Movie Hub