The writers of HBO’s “Game of Thrones” have been known to deliver some shocking blows, but none like those featured in the Season 6 finale. The 69-minute episode was packed with death, drama and, of course, one jaw-dropping revelation about Jon Snow’s (Kit Harington) parents.

Fans of “Game of Thrones” have been speculating about who mothered the bastard of Winterfell for quite some time. Writers introduced him to the show as Ned Stark’s (Sean Bean) illegitimate son. His mother was thought to be a commoner who gave birth to him in the south. That did not, however, stop fans from theorizing about his real origins, with many certain he was the product of Ned’s sister, Lyanna (Cordelia Hill), who was kidnapped and raped by Rhaegar Targaryen, the eldest son of the Mad King. This theory has become known as R + L = J on the internet, though it was largely unconfirmed until “Winds of Winter” aired on Sunday.

During the show, Bran (Isaac Hempstead Wright), now acting as the three-eyed raven, traveled back in time. He stops at a place known as the Tower of Joy — a name given to the structure by Rhaegar Targaryen. There he sees a younger version of his father battling with three members of the King’s Guard. While the fight ensues a woman, only identified as Ned’s sister during the Season 6 finale, can be heard shrieking from within the stone walls. Bran visited this vision once before, but was stopped from viewing it in its entirety because, according to the former three-eyed raven, he wasn’t ready. When he finally harnesses his powers enough to revisit it, he learns some shocking information that shakes up everything he grew up being told about his half-brother Jon.

Rhaegar has played an important role in “Game of Thrones,” though he has never actually been shown. The actions of his father while seated upon the Iron Throne continue to affect those vying for it on the show — especially Rhaegar’s sister, Daenerys Targaryen (Emilia Clarke), the Lannisters and the remaining Stark children. Following Sunday’s apparent confirmation, it appears the Prince of Dragonstone will continue to be a key figure on the show despite his absence, so fans should probably get acquainted.

Below is everything we know about Rhaegar Targaryen and the R + L = J theory:

Rhaegar Was the Mad King’s Heir:

At present Daenerys is the only known living member of the Targaryen family on “Game of Thrones,” but there was once a time when their lineage was strong in Essos. Rhaegar was one of the Mad King, Aerys Targaryen’s, three children from his marriage to his sister, Rhaella Targaryen. Rhaegar had both a brother/cousin, Viserys Targaryen (Harry Lloyd), and a sister/cousin, the Mother of Dragons. He was also related to Maester Aemon (Peter Vaughan) of the Night’s Watch, who died during Season 5, episode 7. The wise old man was said to be his great uncle. Rhaegar was known to have two children — Rhaenys and Aegon Targaryen.

He Was, at One Point, Set to Marry Cersei Lannister:

Tywin Lannister (Charles Dance), father of the current Queen of the Seven Kingdoms (Lena Headey), once wanted his daughter to marry Rhaegar. As fans of “Game of Thrones” now know, there is a longstanding feud between House Lannister and House Targaryen, which stems from this failed arrangement. The Mad King is said to have suggested that Cersei was an unfit match for his son, instead choosing a dornish woman named Elia Martell. As Oberyn Martell (Pedro Pascal) reminds the Lannisters during his Season 4 visit to King’s Landing, Elia’s two infant children were killed in front of her by Ser Gregor Clegane (Conan Stevens). He then raped and killed her.

Rhaegar Kidnapped and Raped Lyanna Stark:

During the Prince of Dragonstone’s marriage to Elia Martell, he kidnapped and raped Lyanna Stark, Ned’s sister. Brandon Stark rode on House Targaryen to demand Lyanna be freed, which prompted the Mad King to have both him and his father, Rickard Stark, killed. This action gives House Stark the fuel they need to rebel against the Targaryen family. Joined by Robert Baratheon (Mark Addy) — who was slated to marry Lyanna — the Starks fight valiantly in the War of the Usurper, also known as Robert’s Rebellion.

Although it is widely believed that Rhaegar took Lyanna against her will, it is not the only theory about their relationship. Some “Game of Thrones” fans believe that the pair were in love and ran away together.

Lyanna Became Pregnant After Her Kidnapping:

As is evident from the Tower of Joy scene, Lyanna became pregnant and gave birth after she was taken and raped by Rhaegar. She delivered her child — a baby boy — in an isolated and heavily guarded tower while Rhaegar was out on the battlefield. Ned Stark arrived on the scene, killing the guards. He then rushed to the top of the tower to find his sister fighting for her life. Before dying she shared a secret with her brother, which was inaudible during Season 6, episode 10 of “Game of Thrones.” The context, however, suggests she revealed the paternity of her son. While much of her secret remains under wraps, she was heard asking that her brother promise to care for the child and protect him from their father’s wrath.

He Was Killed by Robert Baratheon:

Rhaegar was killed during Robert’s Rebellion in the Battle of the Trident. He and Robert Baratheon ound themselves in a duel, during which Rhaegar met his end.

If Jon Snow Was Rhaegar’s Son, He Is the Rightful Heir to the Iron Throne:

During the “Game of Thrones” finale the Bastard of Winterfell was named the leader of House Stark and the acting King of the North, but should his lineage check out he may have a much higher claim in the Great Game. At the time of his death, Rhaegar Targaryen was the heir to the Iron Throne. He and the rest of his family were killed shortly after (except, of course, Daenerys and Viserys). With Rhaegar’s brother dead and Jon potentially being the last male Targaryen, he could realistically make a claim for the highly coveted position in the seven kingdoms — but would he?

“Game of Thrones” Bran learns that his Aunt Lynna (Cordilia Hill, right) may have mothered his half-brother Jon Snow (not pictured) by visiting a scene from Ned Stark’s (Robert Aramayo, center) past during Season 6, episode 10, of “Game of Thrones.” Photo: HBO