Prince John Constantinovich of Russia () (5 July 1886 – 18 July 1918), also known as Prince Ioann, Prince Ivan or Prince Johan, was the eldest son of Grand Duke Constantine Constantinovich of Russia. He was described as a gentle, religious person. His relatives gave him the nickname of Ioannchick. He was born at Saint Petersburg, Russian Empire, and was in the House of Holstein-Gottorp-Romanov. He later married the Princess Helen of Serbia.