Historical Incest

When it came to incest and keeping bloodlines pure among royalty and all that craziness, I always mostly heard about the Hapsburgs

Today I found out that Cleopatra was incredibly incest born. I saw her family circle and it's so gross and awful.

Hapsburg was always described as incredibly, morbidly disfigured, infertile, and limp due to the damage in his DNA.

Yet Cleopatra was always described as beautiful and a powerful seductress who was able to seduce Julius Caesar himself.

How is that possible? I'm genuinely curious.