This is fucking crazy. If a woman has a child with a man, his DNA remains inside her for life AND if she has a kid with another man, that previous mans DNA is fucking transferred to the new kid from a different father. The father's DNA (via fetal cells) can remain in the mother’s body for decades and potentially for life, through a process called fetal microchimerism. Cells from a previous pregnancy (including those carrying DNA from the earlier father) can transfer at low levels to later children via the mother. The later child can end up with a number of cells that contain DNA from the former father. Those cells originate from the older half-sibling (the previous pregnancy) and can be passed through the mother. This is a form of microchimerism.