Nicholas Alexandrovich, Heir, Tsesarevich and Grand Duke of Russia (Russian: Цесаревич Николай Александрович, Наследник-Цесаревич и Великий Князь) (20 September [O.S. 8 September] 1843 – 24 April [O.S. 12 April] 1865) was Tsesarevich—the heir apparent—of Imperial Russia from 2 March 1855 until his death in 1865.

Born at the Alexander Palace in Tsarskoe Selo and nicknamed "Nixa", he was the eldest son of the Tsesarevich Alexander Nikolaevich, eldest son of Emperor Nicholas I, and the Tsarevna Maria Alexandrovna of Russia. In 1855, his paternal grandfather died, and his father succeeded to the throne as Emperor Alexander II.

In the summer of 1864, Nicholas became engaged to Princess Dagmar of Denmark. She was the second daughter of King Christian IX of Denmark and Princess Louise of Hesse-Kassel and was a younger sister of the Princess of Wales, later Queen Alexandra and wife of the heir-apparent to the British throne, Albert Edward, who reigned as Edward VII.

Until 1865, Nicholas was thought to have a strong constitution, but early in that year, during a tour in southern Europe, he contracted an ailment that was initially incorrectly diagnosed as rheumatism. Nicholas's symptoms at that time included back pain and a stiff neck, as well as sensitivity to noise and light. He thought little of his ailments, however, and continued his tour in Italy.

His health rapidly worsened, and he was sent to Southern France, but this move brought him no improvement. It was eventually determined that he was suffering from cerebro-spinal meningitis, and it was speculated that this illness of his was caused by a previous accident in a wrestling match, in which Nicholas participated and was thrown down. In the spring of 1865, Nicholas continued to decline, and he died on 24 April 1865, at the Villa Bermont in Nice, France.

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