Although raised early in military fashion and sent off to serve in the Imperial Russian Navy and the Imperial Guards, the Grand Duke was more interested in literature and art. When he finished his tour of duty, he settled in St. Petersburg, marrying his second cousin, Princess Elisabeth of Saxe-Altenburg and moving into the Pavlovsk palace. Though they went on to have nine children and become one of the few couples close to Czar Nicolas II and his family, due in part to the Grand Duke’s serious nature – he wasn’t the typical Russian noble playboy – Grand Duke Konstantin Konstantintovich was secretly bisexual, a fact which came out when his diaries were published after his death. The diaries detail his visits to St. Petersburg brothels and his many affairs with men starting with his time in the Imperial Guards and throughout his marriage.
The Grand Duke was a great patron and respected intellectual – he was a friend of Tchaikosvky and chairman of the Russian Musical Society, as well as president of the Russian Academy of Sciences. He was also an honorary member of the Royal Swedish Academy of Sciences. He wrote a number of poems and plays, and translated Goethe, Schiller and Shakespeare into Russian.
When the First World War broke out, the Grand Duke and his wife were in Germany, where they were considered prisoners. After the Grand Duchess petitioned the German imperial couple, they were allowed to return to the closest Russian station. By 1915, the Grand Duke’s son-in-law and fourth son had been killed in the war, and the Grand Duke himself died June 15, aged 56.
The Grand Duke Konstantin Konstantinovich Romanov has a page on Wikipedia, here.