Eleonore Caroline Gasparine Louise, Princess Reuss-Köstritz, was Tsaritsa of Bulgaria and the second wife of Tsar Ferdinand of Bulgaria.

Born in Trebschen on 22 August 1860, Eleonore was described as "a plain but practical... capable and kind-hearted woman".

Following the death of his first wife, Marie Louise of Bourbon-Parma, Ferdinand sought another wife to carry out the official duties required of the consort of a head of state. As a gay man with no requirement to produce further heirs, Ferdinand stipulated to his assistant that he wanted a bride who did not expect affection or attention. A list of candidates was whittled down to Eleonore and she and Ferdinand subsequently married in Coburg on 28 February 1908. Initially entitled Princess of Bulgaria, Eleonore assumed the title Tsaritsa on 5 October 1908 following Bulgaria's declaration of independence from the Ottoman Empire.

Eleonore had presumably been carefully pre-informed of Ferdinand's sexual preferences and it is debatable whether the marriage was ever consummated. Certainly, Ferdinand demanded separate bedrooms for he and Eleonore while guests of King Carol I of Romania during their honeymoon. As it was, Eleonore remained neglected by Ferdinand throughout their marriage, leaving her to raise her step children and devote herself to the welfare of the Bulgarian people. Eleonore came into her own during the Balkans and First World Wars when, working tirelessly as a nurse, she was a cause of great comfort for many injured and dying Bulgarian soldiers. It was said that she had "a special gift for relieving suffering".

Tsaritsa Eleonore became seriously ill during the final years of WWI, dying in Euxinograd, Bulgaria on 12 September 1917. Her last wish was to be buried in the cemetery of a 12th century church at Boynara, near Sofia. This was granted.