@Psycada
He's referring to himself, that he will keep fighting no matter what, while talking to his son: "But until the end, Father (your father) will fight."
In the previous square he was referring to the fact that they have only about 5 minutes left, which confirms it :
"We have about 5 minutes left". "But until the end, Father (I / your father) will fight."
Saying "a father" makes no sense in that context.