Although the character died before the events of the show, he plays a huge role in the series as the brother of the Queen of Dragons, Daenerys Targaryen, and is widely believed to be Jon Snow's father.
The identity of Jon's parents is one of the most discussed Game of Thrones topics, and in the latest episode it was basically confirmed he was conceived by Lyanna Stark and Rhaegar, after he annulled his first marriage.
Fans are expecting to see a flashback to Rhaegar's time in season 7, and have therefore begun to speculate about who might portray him on screen.
Two months ago a Reddit user posted about how The Fall and Clique actress Aisling Franciosi had started following a Welsh actor called Wilf Scolding on Twitter. Franciosi plays Lyanna Stark, Jon's mother, on the show, and was shown briefly when Bran went back to witness Jon's birth.
Scolding graduated from drama school in Wales and voices Chris Carter in BBC radio show The Archers. He recently went on a Game of Thrones following spree which included Franciosi, Liam Cunningham, who plays Davos Seaworth in Game of Thrones, and the official Game of Thrones account.
A more recent post claimed that the HBO leaks, which happened when hackers broke into HBO's computer network, confirmed the news by placing Scolding on the casting list under "Rhaegar".
In the latest episode, Gilly was reading from an old diary with Sam when she found an entry about someone called "Prince Raggar" who married someone during a secret Dornish ceremony.
Fans believe this suggests Rhaegar married Lyanna Stark, meaning that Jon Snow is not a bastard, as he currently believes, and could give him a bigger claim to the Iron Throne than Daenerys.
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