
When does Louis tell Alexa that it’s his baby?

Do you mean when does Maetel tell Louis it's his baby?
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SPOILERS BELOW
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He doesn't. Louis finds out from the blonde woman that Maetel almost slept with that night, the woman that Maetel ordered out of the carriage once he saw Louis.
At the end of chapter 46, Louis goes to ask Maetel why he didn't say anything. I presume that in chapter 47, we'll find out why Maetel kept quiet.
WHY DID IT HAVE TO BE HIM