[@Holy Soldier] Oh cause I was pretty sure is was more like Circe Lannister is now the [i]dowager[/i] queen. 

So if Tommen died (and was not married to Marjorie, and Marcella was still alive). 

Marcella would become queen of the seven kingdoms. 

So Line of succession was Joffery, Tommen, and then Marcella: if her brothers had no children.

Because otherwise If Circe was lawfully the Queen by right, then if she where to marry, any sons born from that union would be king before Marcella. Even though it was King Robert Baratheon who is the true Royal line. 

----------------------------------
I know this is a male-preference primogeniture, but after all is said and done, Madeline has no legitimate brothers, so she is the rightful heir of King Samson. So I assumed that Queen Margaret becomes a dowager Queen, and Princess Madeline as the only heir, becomes the rightful ruling Queen, after a proper coronation. On the other hand if in this AU, female heirs have no rights to the throne after their brothers, then King Samson's brother Stuart would become King.
---------------------------------- 

[color=fff79a]"To make it simple, remember The Lion King? Scar killed Mufasa and then tried to kill Simba so that he could be the King because he would be because of his blood. If Simba died, and Scar died, then the Queen would be Simba's mother all on her lonesome. If Nala had married Simba before he died, and then Simba's mother died, then Nala would be the queen."[/color]

See in your scenario I was under the impression that King Mufasa is dead, and Prince Simba is [i]considered[/i] dead/missing? So Scar would be rightful King by blood. Simba's mother is a dowager queen, without any power. If Simba had a younger sibling then he/she would be king/queen.  

--------------------------------