Jeanne d'Albert, daughter of Henry II, king of Navarre dies few hours after giving birth to her son Henry (OTL Henry IV of France) who still is healthly child in this TL . So the newborn will be heir to the throne of Navarre since his birth, and king of Navarre after his grandfather dies in may 1555, leaving 1,5 years old grandson on the throne. So in such situation would a Henry's father Antoine became regent? Antoine was not very religious, changing confession was not problem for him-he reconverted to Catholicism IOTL and fought Hugenots. Henry, raised by his father would likely remain Catholic, his uncle Louis would be main leader of protestants, but he was further in succession line. So assuming minimal butterflies France has Catholic heir to the throne after Valois extinction. What would be effect of such change? St. Bartholomew Day massacre is certainly butterflied away, and Catholic League has less support without fear of Hugenot taking the throne.