Athos-Cosette relationship

The relationship between fellow Musketeers Athos and Cosette D'Artagnan was originally a strained one that eventually evolved into a friendship and then a strong brother/sister relationship.

Series 1
Like the original, Cosette thought Athos killed her father and rendered her an orphan and attacked him without hesitation. However, after saving hi slife, Athos appears to have warmed up to Cosette by the end fo the episode, joining her card game with Porthos to prevent Porthos from conning who he calls "[their] new recruit."

During the third episode, Cosette's and Athos' relationship has improved, as they now consider each other friends. However, Cosette finds it irritating that Athos doesn't open up to her like he does with Aramis and Porthos. However, he finally decides to finally open up to Cosette what happened to his wife, something he never shared even with Aramis and Porthos. She promises to him that she won't tell them what happened between them.

In episode five, Athos tells her she doesn't have to continue with him or Aramis to clear Porthos' namebecause the boy he was accused of killing was near her age.

Trivia

 * Athos was the last Musketeer of the Inséparables to know Cosette is a woman.
 * Cosette was first to know that Athos was once married to Milady and his dark secret.