King Tut (Tutankhamun) was married to a close relative. This is what pharaohs in Ancient Egypt typically did. There were at least two reasons for this. First of all, pharaohs were seen as gods. It does not make sense for a god to marry a mortal, and so pharaohs typically married close relatives who shared their status. Scholars also say that pharaohs might have married close relatives as a way of ensuring that power stayed in their family. If they married outside the family, some of the power could end up with their spouse’s family rather than their own.
King Tut married a woman named Ankhesenamun. According to the article in the link below, her exact relationship to King Tut is not completely clear. She might have been his half-sister or she might have been his niece. This couple appears to have had two children, both daughters who were stillborn.