So.. ahh.. err..umm... Euron and Jamie have NOT finished their conversation yet.
Ahem... (*clears throat*)
For some reason... I think Cersei told a
BOLDFACE LIE to Jamie tonight.
Because I'm thinking that
Euron 
is the actual Father of Cersei's new (unborn) child... Not Jamie.
In these 2 scenes below...
- Cersei is showing that she is 'a few steps' ahead of Jamie... about certain things.
- Even when faced against outrageous odds... she was ready to DIE, earlier in the episode... and was angry that Jamie wasn't also.

- And she was 'seething' because she felt Jamie betrayed her for meeting with Tyrion.
- But it was her SUDDEN change in temperament, in this 2nd clip, later in the episode.

- She didn't expect to get pregnant by Euron. (That's why 'Doctor Qybyrn' keeps visiting her room)
- Now she is thinking like Tywin... and exploiting the situation to her advantage.
Think about it...
- Cersei managed to keep Robert Baratheon
'in the dark' about Joffrey, Marella & Tommen... for YEARS.

- Therefore, I think she ALREADY slept with Euron

... and Jamie is just playing catch-up.

- But Euron is prolly gonna let Jamie know it... in the
MOST DISRESPECTFUL manner possible.

- And it will be the 2nd part of their 'brotherly conversation'.
Wait for it.
Ask yourself...
Where was Euron while Jamie was escorting the Tyrell Gold back to Kings Landing... and dodging all that Dragonfire?
Last we seen him... he was attacking the Unsullied ships at Casterly Rock, in episode 3.
If he got to Casterly Rock 'so quickly'... then surely Euron could have ALSO sailed his speedy battleships back to Kings Landing BEFORE Jamie could escort hundreds of very slow-moving / extremely heavy wagons full of grain... while Bron was
'convincing stubborn farmers to surrender their harvest' along the way... plus managing THOUSANDS of Lannister soldiers... who are literally MARCHING ON FOOT across Westeros.
That whole caravan was moving so slowly... that Dany actually had time to sail her Dothraki Army down from Dragonstone... then around the bend (probably into Storm's End, since they didn't go through Blackwater Bay, right past Kings Landing

)... then stampede across the land to
'cut them off at the pass' before they reached Blackwater Rush. (Right before Dany attacked, Randyll Tarly tells Jamie: "We need to get the last of these wagons over the Blackwater Rush before nightfall" - So you can kinda tell where they were on the map below)
If Dany could move 'that fast' across water... then Euron could move MUCH FASTER across water.
Just my opinion.