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Original Description:
 
if you were wondering, nautical mile’s other mother is a seapony named angelfish. she and twilight met at a seaquestrian meetup about magical artifacts. they had an excellent discussion and ended up meeting again to talk some more. angelfish developed a massive crush on twilight, which she reciprocated. they ended up having a little fry by the name of nautical mile.  
twilight was worried about her daughter being forced into the limelight (she had seen what happened to her niece) and decided that she ought to be raised by angelfish in seaquestria, as they didn’t care as much about equestrian princesses.
 
angelfish and twilight have an open relationship, and although they may spend most of their time apart they still love eachother dearly.