Any Royal child born at Windsor castle is illegitimate. This is true all the way back through the English Royal families family tree. The Royals used a Windsor Castle birth as a code for illegitimate child. Windsor sounding like Windsire. The idea being that the wind sired the royal family (eg a bastard child).

The British Royal family knew that all their inbreeding was causing serious genetic problems. Many of their men were impotent. Having bastard childen was not an accident but an intentional plan to reduce genetic disease in the Royal Family. They didn't think of it in terms of genetic disease, but the issues were the same. They realized they needed to have blood outside of the royal family for their children to survive more and be less frail.

Windsor Castle has been in use since circa 1000 AD. This is when the Royal Family started to have a lot of problems with inbreeding and infertility. The Year 1000 was a bad year in global history. The Catholic Church was falling apart as Popes kept getting killed. The illuminati system was collapsing underneath the weight of inbreeding and the black death.

Windsor Castle was part of the illuminati plan to keep the French Jews in control of England by allowing for bastard children. While they allowed for bastard children, the point of having a Windsor birth was so all the Royal Family would know they weren't really 100% Royal and thus should be excluded from power.

William the Conqueror who conquered England for the French and built Windsor castle was himself a bastard child and known as William the Bastard. William was a French illuminati Jew who was also impotent because of genetic disease. His sons were all bastards like him, which is why he had trouble controlling them.