In Season 6, Game of Thrones introduced a new member of the Greyjoy family: Euron Greyjoy, murderous uncle to Yara and Theon. Euron plotted his way into wresting control of the Iron Islands away from Yara at the Kingsmoot after killing his brother to open up the king spot in the first place. It's clear that Euron will do whatever it takes to seize power and he doesn't care who he hurts in the process, even if his family are the first to suffer. Based on that description, it sounds like Euron would have a lot in common with another questionable ruler in Westeros: Cersei Lannister. They're both ruthless and power-hungry, and if they met it could be the beginning of a beautiful (horrible?) friendship. But will Cersei and Euron Greyjoy team up on Game of Thrones?
It seems like a real possibility. Euron is clearly interested in forming alliances, because in Season 6 he swore he'd join forces with Daenerys through marriage. That never came to pass (thankfully) so Euron might turn his attention to the other single female ruler around. They could be politically advantageous to each other, plus they have similar outlooks on life and Cersei does like to employ an unhinged killer or two. It's hard to say for sure, but there are some hints that Cersei and Euron will team up.
Actor Pilou Asbaek, who plays Euron, seemed intrigued by the possibility when he spoke with Entertainment Weekly. Apparently Euron will try to form an alliance with Cersei, though she might not be open to it. "For Euron, the question is, 'Who gives me the best odds?'" Asbaek said. "Is it the dragon mother? No. Is it with Cersei? I think it is. Dany is still trying to be a good, decent, honest person. Cersei sold her soul many years ago. Maybe that's why Euron likes the idea of her."
An upcoming episode description from Season 7 could point towards Euron taking steps to win Cersei over, too. In Episode 3, "The Queen's Justice," Cersei "returns a gift," whatever that means. It's possible that the gift in question was sent by Euron to try and sway Cersei to his cause. It's unsurprising that she would be reluctant, at least at first. Cersei has already faced so many threats to her position that she'd likely be wary of someone else trying to take away her power.
Euron will almost definitely try to join Team Cersei, but whether she'll be convinced down the line is anyone's guess. Fans will be able to find out soon enough when Game of Thrones returns on Sunday, July 16.