Princess Marie of Hesse and by Rhine (Prinzessin Marie Viktoria Feodore Leopoldine von Hessen und bei Rhein, 24 May 1874 – 16 November 1878), was the youngest child and fifth daughter of Ludwig IV, the Grand Duke of Hesse and his first wife Princess Alice of the United Kingdom. Her mother was the second daughter of Queen Victoria and Prince Albert of Saxe-Coburg-Gotha. She died of diphtheria at the age of four and was buried with her mother, who died a few weeks later of the same disease. She and Queen Victoria shared the same birthday.

She had six older siblings, Victoria, Elizabeth, Irene, Ernest, Friedrich, and Alix. She was known as May in the family. When she was a baby, her mother remarked in a letter that "little sister Maly" bore a strong resemblance to her dead brother Friedrich ("Frittie") at the same age "with such quick eyes and two deep dimples in her cheeks." A few weeks later, Alice wrote that baby "Maly" had fair skin, light brown hair and deep blue eyes. As she grew older, she smiled frequently and Alice thought she more strongly resembled her older sister Victoria, with "fair hair, marked eyebrows and speaking eyes." She and her sister Alix, two years older, "made a pretty contrast." Her mother thought her youngest child was "enchanting" and as a toddler the little girl called her mother "my 'weetheart." Alix was her constant companion. The two girls were dressed alike and shared the nursery. The family enjoyed a trip to the seaside in the summer of 1877 and the two youngest girls were a source of delight to their mother. Sending photos taken then to her mother, Queen Victoria, Alice wrote that "May has not such fat cheeks in reality; still it is very dear. The two little girlies are so sweet, so dear, merry, and nice. I don't know which is dearest, they are both so captivating."

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