#59 - headcanon - Rae
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After Diego and Amy had Rose, they had a baby named Rae. Rae only lived two weeks before they died, leaving Amy and Diego very heart broken. They tried again with Tyler, making his middle name Rae, and upon learning about Tyler's heart problems at the age of 7 or 8, Amy and Diego were willing to go through any kind of debt to make sure Tyler got the medical attention he needed to live.
Tyler nor Rose have any idea about their sibling and likely never will.