Hittite Law of Succession
The position of the king in the early Hittite state does not
appear to be very secure. One of the first recorded events in Hittite history is
the nomination by the nobles of a rival king to Labernas, who's father had
designated him as his successor. Subsequent history is full of revolts and
rebellions on the part of the king's family with the king constantly struggling
to preserve the peace.
The death of a king caused a constitutional crisis. A wise monarch would try to
avoid this by appointing his successor. Royal succession was finally regulated
by King Telipinus, who enacted the following law:
Let a prince, the son of a wife of the first rank, be king. If there is no
prince of the first rank, let one who is a son of the second rank become king.
If, however, there is no prince, let them take a husband for a daughter of the
first rank and let him become king.
This act of legislation marked a major turning point in Hittite history. What
once was a kingdom subject to recurring crises, now became a stable environment
and history indicates that the king was never again challenged by ambitious
noblemen. So successful was this law that approximately 200 years later when
King Muwatallis died without a legitimate heir, the throne passed to Urhi-Teshub,
the son of a concubine, without incident. Of course he was later deposed by his
uncle Hattusilis for insolence and incompetence.
A footnote......Labernas appears to have been a royal title rather than a name
in the early days of Hittite history.

The Hittites, O.R. Gurner
Ancient Mesopotamia, A. Leo Oppenheim
Cultural Atlas of Mesopotamia and the Ancient Near East,
Michael Roaf