Regretable vs Regrettable - What's the difference?

As an adverb regretable

is an alternative spelling of regrettable.

of an event, action, or state, allowing or deserving regret.

(en adverb)

* The spelling regrettable is more common.

(en adjective)

Of an event, action, or state, allowing or deserving regret.

His painting his name of my car was more than regrettable , it was criminal.

It was regrettable that the teacher made the class retake the test when he was wrong about the answers.