The Throne (2015)

Yi San, later King Jeongjo (Lee Jun Ho) was the son of Crown Prince Sado and grandson of King Yeongjo .
So, if you want to know what happened between Crown Prince Sado (Yoo Ah-in) and King Yeongjo (Song Kang-ho) then this is the movie for you.

Sungkyunkwan's scholars help prince Sado's son to clear his father's name and find lost important document. It's totally different story, but you can learn another version of prince Sado's tragic story.
If you liked prince Sado as a history character, you should watch this drama. (from this drama I first heard about prince Sado and since then he is my obsession)

The protagonist this, King Jeongjo filme is a Prince Sado son's and it's a continuation of the filmd Sado, basically.

Yi San is a 2007 drama about Sado's son. It covers about the same time period as the more recent Red Sleeve 2021 drama except that it has greater focus on politics. If you want to watch a drama which shows more focus on Sado's son's politics as a prince then as a king, Yi San 2007 drama is the show for you. Yi San 2007 also shows more on how Sado's son was acting as his father was dying in the beginning episodes.
For Yi San fans, you can watch in The Throne another portrayal of how Yi San's father died.

For my taste the throne is better because it's just 2 hours but more or less enough to understand this twisted son-father relationship but the throne it's about the same character "Sado" and how he was killed by his own father

In both Jang Ok Jung and The Throne, we see Yoo Ah In playing a Joseon Royal. King Sukjong (Yoo Ah In's character in Jang Ok Jung) is also one of the main characters in Jang Ok Jung. This means that Jang Ok Jung is a show that might be enjoyed by The Throne fans since it has both Yoo Ah In plus the audience get to know more about King Sukjong (who is only barely mentioned in The Throne). One must keep in mind that Jang Ok Jung has a little twist in that it tends to be more sympathethis towards Sukjong's concubine Jang Ok Jung, who is more historically known as the more villainous concubine. Jang Ok Jung is the mother of the brother of Prince Sado's father, King Yeongjo.

I recommend Dong Yi for The Throne fans since it gives character to the mother of King Yeongjo, the woman who was only mentioned as a lowly concubine in The Throne. Dong Yi is the love story of Yeong Jo's parents as well as the political happenings during Yeongjo's father King Sukjong's era. Dong Yi also shows the rivalry between concubines including Dong Yi (Yeong Jo's mother) and Jang Ok Jung (mother of Yeong Jo's brother, who was the king before him as mentioned in the drama). Through watching Dong Yi, the audience will understand why some people in The Throne think King Yeong Jo killed his brother for the throne as well as how Dowager Queen Inwon was Queen Dowager despite her not being King Yeong Jo's mom.
For Dong Yi fans, The Throne movie shows one tragic aspect in the long reign of Dong Yi's son Yeoning aka Yeong Jo: the events that lead Yeong Jo to put his son Sado in a box which led to his son's death.

=> Both are high profile sageuk projects starring Yoo Ah In
=> Both were shown in 2015 (Six Flying Dragons ended in 2016)
=> Yoo Ah in won many awards for his portrayal in both sageuk projects
=> Yoo Ah In's role has a similarity in both dramas, he's someone who doesn't obey his father's wishes.
=> Because of the success of these two projects (along with Yoo Ah In's 2015 movie Veteran), 2015 was called "A-in-shi-dae" (Ah In era).

The Royal Gambler is about King Yeongjo's early life and his succession to the throne and The Throne has the events that came later in his life.

Another true story about Prince Sado. Both were sad and depress. Great casts and grest acting overall

Both are critically acclaimed historical films from director Lee Joon Ik. These films tell the stories of controversial Joseon royals and focus primarily on exploring character and relationships, rather than politics.

Both are historical films set in the Joseon period. Though The Throne tells a personal story about the strained relationship between a father and son and The Fortress a political one about leadership when faced with no favorable options, I felt that there was some similarity in the atmospheres of these films. While not entirely bleak, these are films that explore human struggles when the tragic end is all but assured. They are both beautifully crafted, elevated by the performances, soundtracks, and cinematography.