This post contains spoilers from the Game Of Thrones Season 7 finale. Tonight's finale of Game of Thrones Season 7 gave us a triple whammy: birth, sex, and marriage. That we would return to the birth and find out Jon's name was a given. That Jon and Dany would do the deed was also in the cards. Marriage? Didn't see that coming. But Bran's voice over brought up an interesting point: Was Robert's Rebellion based on a lie?
Perhaps we should have seen the wedding coming. (Do we have a nickname for it yet? Can we call it "The Golden Wedding"?) After all, the last Game of Thrones episode with a title that matched "The Dragon and The Wolf" was "The Lion and The Rose" and that was the Purple Wedding episode. Also, everyone assumed the title was referring to Daenerys (The Dragon) and Jon Snow (The Wolf). But really it was referring one generation back, to the union of the Dragon (Rhaegar) and the Wolf (Lyanna). If it was really about Dany and Jon it would have been "The Dragon and The Dragon."
But here's the thing: Crown Princes don't annul marriages and get remarried right away to other people with nobody knowing about it. People would have known. Robert would have known.
When Crown Princes marry, it's a big honking deal because succession is on the line. Elia Martell, Rhaegar's first wife, had two children already, one of whom was a son. For him to annul their marriage to marry someone else, who hasn't even proven she can birth male heirs, is a dicey choice. If Aerys had been in his right mind, he would have forbidden it.
Of course, that's one part of this problem: Aerys wasn't in his right mind. And there was a war on, so news can get lost. The Martells were the Targaryens' only allies, one can see why Tywin ordered the news from getting down there until the war was over.
But there is no way that Elia's marriage was annulled and people in the Red Keep -- like Varys, like Tywin -- didn't know. For example: Tywin's excuse to Oberyn, when he accuses the elder Lannister of ordering the Mountain to kill his sister. In the TV show, Tywin simply says he didn't give the order. In the books, though, he gives a bit more detail: He did say to kill Elia. He only told the Mountain to kill the children, because he needed to prove loyalty to Robert. The Mountain took it upon himself to rape and kill her.
He didn't bother to say anything about Elia because "she was nothing." If Tywin thought Elia was still the wife of Rhaegar, there's no way he would have called her nothing. She could have been used as a symbol of the counter rebellion, led by the Martell clan. He would have had the Mountain kill her straight off.
The only reason he didn't bother is if... she wasn't Rhaegar's wife anymore, and everyone in the Red Keep knew it. And moreover, he didn't bother because he knew Robert knew there was no reason to kill her either.
Robert was in command of an army that was comprised of every House in Westeros, save Targaryen and Martell. You don't run an army of that size without having a serious spy network. Yes, Varys and his little birds technically worked for Aerys up until the sack of King's Landing. But his network would have known. And word would have gotten to Robert as well.
This also explains why Ned Stark was so freakish about keeping Jon Snow's parentage on lock. He didn't even tell Catelyn. She went to her grave believing Ned cheated on her during the Rebellion. Most assume Ned kept it quiet because Robert would have killed any Targaryen bastard begat by Rhaegar with his beloved.
But what if Ned kept it quiet because Robert knew Lyanna and Rhaegar were married? And if anyone for a second thought this might be their child, Robert would be staring at the reality he could never face: that Lyanna never loved him, that she married Rhaegar instead, and this was the rightful heir to the Iron Throne. (Not to mention that anyone who might want to stage a rebellion against Robert would snatch Jon up in a heartbeat. No wonder he wanted Jon to go to the Wall, Maester Aemon style).
When the war was over, and Rhaegar and Lyanna were both dead with "no issue," and Elia and her children murdered, one could understand why Tywin, Varys, and others would be all too happy to bury the past at Robert's behest. Did it really matter who was married to whom at that point? Let the winners write the history and forget the past... until now.