Lorelai had twins Instead when she was 16 but when she left she could only take one unable to take both if them being so young She took Rory instead leaving Blair to be left behind and didn't look back not reaching out to her parents for 16 years. Blair Gilmore would grow up thinking Emily and Richard are her parents and grow up in there society and attend Chilton, But on the week of Blairs Coming out / Cotilion the truth would be revealed and what would her future be like knowing her true origin. What would happen when Blair runs away without telling anyone where she's went and doesn't show up until years later. Rory would grow up in Starshollow attending Starshollow high school, Lorelai told Rory the truth once Rory had turned 16. Shows both sides Blairs life and Lorelai and Rorys until the truth is all revealed.
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