Like his older brother Alexander, Constantine was taken by his grandmother to be brought up under her supervision. This was probably the reason why they grew up very close to each other. Once they started to grow up they were allowed to visit their parents at Gatchina, where Costantine acquired the passion of his life, the army. 
From 1792 on, their father was suspicious of their loyalty as he was aware that his estranged mother, Empress Catherine the Great, was considering making Alexander her heir by bypassing Grand Duke Paul. At sixteen Alexander was married to Princess Louise of Baden and Constantine at seventeen to Princess Juliane of Saxe-Coburg-Saalfeld. 
However, Constantine and Juliane, or Grand Duchess Anna Feodorovna, did not get on very well. Constantine was licentious, had many affairs and was described as "rude, impossible, totally lacking in tact". 
According to a sister-in-law, Constantine was "an ugly caricature of his father". The Russian nobles detested him as he was ruthless and a rigid disciplinarian. 
After only about five years, Grand Duchess Anna left Constantine and a few years after that, in 1808, gave birth to a son (Eduard von Loewenfels) fathered by Constantine's brother, Emperor Alexander I. In 1803 Constantine suggested a divorce followed by a marriage for him to 
Princess Janetta Chetvertinskoi, but his mother dissaproved of both suggestions. 
Just as his estranged wife had given birth to an illegitimate child, he, too, fathered an illegitimate son in the same year. However, even after Grand Duchess Anna had left for Europe, they would 
meet regularly and there was even talk of a reconciliation; but finally they would divorce in 1820. 

During his father's reign, Constantine became aware of his father having punished an officer unfairly and went to his father asking him to pardon the officer. Emperor Paul not only did pardon the officer but also reinstated him with a promotion. 
Constantine was not aware of the plotting and subsequent murder of his father in 1801; but after the event, his brother became Emperor Alexander I and Constantine became heir presumptive. After the defeat of Napoleon, the Russian part of Poland received a constitution with Constantine as viceroy. In 1814 he arrived in Warsaw which would remain his home for the rest of his life. He lived in the Belvedere Palace with his mistress Josephine Friedrichs, the mother of his illegitimate son. 
First he established a Polish army which, by 1817, consisted of 35,000 men. He was proud of his army and supported the Polish constitution which made Poland almost independent from Russia. 
However, his drill tantrums caused troubles with his officers. When he temporarily reduced two officers to the ranks, five Polish officers committed suicide, considering themselves dishonoured. A sixth officer challenged Constantine to a duel. Constantine, horrified, agreed to the duel. However, when the officer withdrew his challenge, Constantine made peace with him and apologised to the whole regiment. His temperament ranged from jocular to fierce rages and, like his father, he suffered from bouts of insanity. 
Soon after his arrival in Warsaw he fell in love with the Polish Countess Janina Grudzinska who refused to become his mistress. Constantine disposed of Josephine Friedrichs and, after his divorce came through, married Janina Grudzinska morganatically. Emperor Alexander I allowed the marriage on condition that he renounced his rights to the Imperial crown, which he did secretly. Indeed it had been done so secretly that even their younger brother, Nicholas, now heir presumptive, did not know. Constantine wanted it to be made public but Alexander I refused. Constantine remained viceroy of Poland. 
In 1823 there was a conspiracy to assassinate him and, on 19 November 1825, Emperor Alexander I died. Constantine and Nicholas then swore allegiance to each other. In the period of uncertainty that followed, a revolution was attempted in St.Petersburg which became known as the "Decembrist" movement. Emperor Nicolas I put the revolution down and Constantine remained in Warsaw. Constantine spent much of the crown funds as well as his own money on the development of Poland but still many Poles wanted to be totally independent of Russia. In 1830 there was another revolution in France which caused a stir amongst rebellious Polish army cadets. Although they occupied Constantine's palace in Warsaw he still hesitated for two months before taking action. During this time the Polish army joined the revolt, forcing Constantine to involve his Russian troops which crushed the revolt. The Polish constitution was taken away and the Polish autonomy removed. 
Horrified by these events, and halfway during this Polish-Russian war, Costantine died from cholera on 27 June 1831. His widow was received cordially by both Emperor Nicolas I and his wife, then died in November 1831.
 

Source: Leo van de Pas