"I'm a ___, and I didn't even know it!" (4)
I believe the answer is:
poet
(Other definitions for poet that I've seen before include "Bard" , "'Paul Muldoon or Paula Meehan, say (4)'" , "Heaney or Yeats, say" , "Masefield, for instance" , "Eg, Keats or Auden" .)