As far as we know, King Robert Baratheon on Game of Thrones couldn't see the future like a Melisandre or a Bran Stark. But, his speech in season one about what would come to pass if a Targaryen returns to Westeros appears to currently be set in motion.
This week, when Daenerys set the Unsullied to claim Casterly Rock and Cersei desperately clings to power, Redditor pnr32 was immediately reminded of a conversation between Cersei and her late husband Bobby B.
In season one, episode five, Robert lamented on the State of the Seven Kingdoms and how one would fight a Targaryen:
Robert Baratheon: Let's say Viserys Targaryen lands with 40,000 Dothraki screamers at his back. We hole up in our castles. A wise move. Only a fool would meet the Dothraki in an open field. They leave us in our castles. They go from town to town, looting and burning, killing every man who can't hide behind a stone wall, stealing all our crops and livestock, enslaving all our women and children. How long do the people of the Seven Kingdoms stand behind their absentee king, their cowardly king hiding behind high walls? When do the people decide that Viserys Targaryen is the rightful monarch after all?
Cersei Lannister: [pours herself wine and sits] We still outnumber them.
Robert Baratheon: Which is the bigger number, five or one?
Cersei Lannister: Five.
Robert Baratheon: [holds up his left fingers] Five...
Robert Baratheon: [clutches his right fist] ... one. One army, a real army, united behind one leader with one purpose. Our purpose died with the Mad King.
The most important part on the monologue?
"One leader with one purpose."
As Tyrion said in this week's episode, "My sister's armies fight for her out of fear. The Unsullied will be fighting for something greater: they will be fighting for freedom and the person who gave it to them. They will be fighting for you, and that is why they will triumph."
While the Unsullied might not have faced the bulk of the Lannister forces, Tyrion was right about his army's unity and triumph—and so was Robert.
Other people having interpreted Robert's speech as anticipating the season's end, with Cersei's claim failing to unite her army like Daenerys's purpose.
Robert very well could have been spelling out to Cersei just how she'll meet her demise.