From the Department of Redundancy Department comes this little tidbit from a review of the latest book from poet Charles Simic:
Okay, so here’s the deal. According to Merriam Webster, erstwhile means “in the past, formerly,” so it’s not necessary to say someone is the former and erstwhile U.S. poet laureate.
Unless, I guess, you mean they used to be the former poet laureate and now they’re not the former poet laureate anymore because they’re the poet laureate again. It could happen.