Most blamed it on the grief, or that actually taking the throne changed the power somehow. I planted a few rumors to encourage the latter and avoided ever answering the question directly.

[Politics! He's a liar with good hair, what did you expect?]

...He left me. Me, specifically. He was the only person I trusted to help with 'Ardyn' and he never approved of the idea - just didn't know what to do about you and the Scourge any more than I did. Once I could pull the deception off without help, he told me exactly where I could stuff the entire thing and left.