One of Game of Thrones‘ biggest reveals is Jon Snow’s true parentage, as he’s not really the bastard son of Ned Stark. Ned tells this lie to keep him safe from Robert Baratheon, as Jon is actually the legitimate child of Prince Rhaegar Targaryen and Ned’s sister, Lyanna Stark. Robert’s Rebellion is founded on the lie that Rhaegar kidnapped Lyanna Stark, but the two were actually in love with one another. Jon is the result of their union, though Robert Baratheon would kill him if he knew — just as he tried to kill Daenerys and Viserys early in Game of Thrones.

https://screenrant.com/game-of-thrones-ned-stark-jon-snow-targaryen-hair-eyes-what-if-theory/