As River Song would say : Spoilers, sweetie ! ...
Just when Axle Munshine was beginning to think he had already deciphered in his dreams everything there was to know about his cruel future, and now that he is firmly convinced poor Musky is trapped forever in a parallel Universe, out of his reach, Destiny plays yet another trick on our Vagabond of Limbo.
As he pays a formal visit to the Prince of Eternauts, in order to let him know his beloved child Musky has officially vanished from their world, and should be considered dead, Axle, who has come fully expecting to take all the blame for Musky's disappearance, is stunned to find himself face to face with... Musky's carbon copy !
It turns out that Eternauts have the amazing power of cell fissiparturition - they are able to clone themselves at various stages in their lives.
Each clone remains stuck at the same stage, like a perfect 3-D replica of what each individual was like at various moments of their lives : as a toddler, during his or her childhood, during teen years, and so on.
As it happens, Musky had been freshly cloned just before she decided to follow Axle in his endless quest.
And so she left behind « Muskee », her cloned self, like a never-aging twin sister.
Muskee is the reason why the Prince did not stop his only child from running away with Axle : he knew he literally had a heir and a spare, so to speak.
Muskee doesn't merely look exactly like Musky. She is identical to her "twin" in terms of personality, impulsiveness, and in matters of the heart as well.
Their only major difference is that Muskee can never grow older or have children of her own – like many cloned beings, she doesn't have reproductive organs, nor the ability to give life.
Without ever having met Axle, Muskee has remained connected to her « twin sister »'s emotions, and she knows how much he means to her.
Fiercely jealous of the love they shared, she cannot help following the same path as her double ; even though she knows she is just a pale copy of the real Musky in Axle's mind, she feels the exact same urge to follow the Vagabond of Limbo and to link her fate to his, no matter what happens - forever.