/flame ON!
ah, Queen Victoria. one of Britain's more frumpy queens. Empress of India, never even friggin went there.
Inbreeding was common in the Hellenistic era, however politically motivated it may have been. Particularly common was between brothers and sisters, of note Ptolemy II Philadelphos 'the brother-loving' marrying his sister Arsinoe (recorded as Arsinoe II; he previously married an unrelated woman also named Arsinoe, whom he packed off to an island somewhere to marry his sister), arguably to maintain a pure-blood dynastic monarchy begun by his father, Ptolemy I Soter 'the saviour'.
However, the successor Ptolemies got worse in political and military tact, and sadly the last true Hellenistic kingdom eventually became an inert political entity, saved time and time again by Rome's intervention against succeeding generations of Seleucid rulers.
Or maybe it was something in the water

/shrugs
/flame OFF!