He would never qualify for the throne because if he is their son, he's illegitimate.
"The line of succession to the British throne is the order in which members of the royal family would come to the throne if the reigning king or queen died.
At present the first in line is Prince William, Duke of Cambridge and then Prince William's son, Prince George of Cambridge.
Traditionally, males came before females in the line of succession. However, the law changed on 26 March 2015, so at present, for people born after 28 October 2011 the succession is decided only by age: older children come before younger children. This system of inheritance is called absolute primogeniture, as opposed to male-preference primogeniture. When someone who is in line to the throne has a child, that child comes after them and their older children, but before anyone else in the line of succession.
He would never qualify for the throne because if he is their son, he's illegitimate.
"The line of succession to the British throne is the order in which members of the royal family would come to the throne if the reigning king or queen died.
At present the first in line is Prince William, Duke of Cambridge and then Prince William's son, Prince George of Cambridge.
Traditionally, males came before females in the line of succession. However, the law changed on 26 March 2015, so at present, for people born after 28 October 2011 the succession is decided only by age: older children come before younger children. This system of inheritance is called absolute primogeniture, as opposed to male-preference primogeniture. When someone who is in line to the throne has a child, that child comes after them and their older children, but before anyone else in the line of succession.
Excluded from the line of succession are Catholics and** illegitimate children**." https://simple.wikipedia.org/wiki/Succession_to_the_British_throne