Michal Szewczuk, 19, posted extremist material including an image of the prince with a gun to his head on a blood-spattered background, the UK Press Association (PA) news agency reported.
Published months after Harry's wedding to Meghan, whose mother is African-American, the image also featured a swastika and the phrase: "See Ya Later Race Traitor".
He also admitted five counts of possessing material likely to be useful to someone planning a terrorist act.
He was sentenced alongside Oskar Dunn-Koczorowski, 18, from West London, who received an 18-month detention and training order after admitting to two counts of encouraging terrorism, CTP confirmed.
Detective Chief Superintendent Martin Snowden, of Counter Terrorism North East, said: 'Dunn-Koczorowski and Szewczuk clearly see themselves as superior to the majority of society and they feel their duty is to express their beliefs, in turn teaching others'.
Poulet says the posts "are abhorrent as well as criminal by reason of their clear intention to encourage terrorist acts".
Autonomous Domino's pizza deliveries starting later this year
Nuro, for the unaware, is a robotics company that has been trying to "transform local commerce through driverless delivery". The pizza will arrive in Nuro's R2 vehicle, a custom-built autonomous vehicle designed for delivering food and other items.
"The considerable amount of material they have posted on social media channels not only reflects their extremist beliefs but was meant to encourage others to carry out despicable acts", he said in a statement seen by CNN.
Szewczuk made the comment in an an "abhorrent" online post and now has been locked up after the Old Bailey sentenced him to four years and three months today.
Other posts by the men included support for Norwegian far-right mass killer Anders Breivik and backing for the neo-Nazi group, Sonnenkrieg Division.
The defendants were both said to be of Polish descent, but had only known each other through online chatrooms.
His lawyer, David Kitson, admitted Dunn-Koczorowski's mindset had not changed since the offences were committed, quoting from a medical report that said the teenager had a "lack of remorse" for his views and a "deeply entrenched ideology".
Dunn-Koczorowski was just 17 at the time of the offences and was living at home.
Courteney Cox Aka Monica Geller Re-Visits Her Iconic Apartment From FRIENDS and Fans Are Crying Tears of Joy (Watch Video ). Aniston, who played Rachel Green on the mega-hit sitcom, told DeGeneres "You know what, because, listen, I told you this".
Sauf que la performance n'a visiblement pas été appréciée par les téléspectateurs qui ne se sont pas retenus pour le faire savoir. Ce n'est malheureusement pas la première fois que l'artiste s'attire les foudres des internautes.
A man who threw a milkshake over Nigel Farage during a city centre walkabout has admitted common assault and criminal damage. The district judge Bernard Begley said Crowther would not be jailed but would have to carry out unpaid work.
By playing in 55 or more games this season, Conley's $34.5 million contract for the 2020-21 season became fully guaranteed. The Ringer's Kevin O'Connor also recently reported that the Jazz are among the teams expected to pursue Conley.
Thrash metallers Overkill wrote: 'Sending positive vibes to @DaveMustaine who has just been diagnosed with throat cancer. Dave Mustaine of U.S band " Megadeth " performs at the Rock in Rio Music Festival in Lisbon May 30, 2010.
La France a-t-elle reçu un cadeau de l'arbitre?
Ce qui l'est beaucoup moins c'est que l'arbitre a fait retirer le penalty que Renard avait envoyé sur la base du poteau. Wendie Renard a quand même reconnu qu'elle avait eu de la chance: " Heureusement qu'il y a la nouvelle règle! ".
Lyon give Tottenham their price for Ndombele
His driving runs into the box and good passing help his team in the transition phases of the game. His dribbling and passing have been highlighted as being the midfielder's strongpoints.
Newsday, Calls for Hong Kong's leader to resign
Wong said he watched footage of Sunday's protest, in which marchers called for Lam to step down, from his jail cell. Carrie Lam step down. "It doesn't really matter because the next one would be just as evil", said Kayley Fung, 27.