Declaring your relationship in the midst of war was dangerous, unless you were untouchable. They were best kept secret, until it was safe.James Potter thought he could have it all- a marriage to Lily Evans, and a relationship with Regulus Black. Until, of course, he wanted an Heir.
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Hydrus Arcturus Black is born on the 8th of May 1980. Henry James Potter is born on the 31st of July 1980. Two very different boys, with very different lives.
Hermione was not meant to draw attention to herself, so why was she suddenly so involved with the Marauders?
(Or Hermione is reborn as a Rosier in the Marauder's Era and sets out on a mission to change history)