On the death of a King, his heir apparent will turn up as king in the most developed province in your empire/kingdom, which in your case unfotunately happens to be Antioch.

Most developed province: combination of highest level of castle + number of buildings.

To avoid this, the following may be attempted:

1. Firstly, reload so that your king does not die in that turn. BTW this is a bit of an exploit.

2. Secondly, reduce the tech level of antioch to below that of wessex.