I'm a PhD candidate at a UK university.
I believe that normally a candidate's supervisor would be the person to invite someone to be an external examiner for the thesis.
In my particular case, however, my first choice of examiner is someone with whom I have corresponded for several years, although not directly about the contents of my thesis. I am wondering whether, in this situation, it would be odd if I did not either ask them unofficially directly myself, or at least given them a heads up that my supervisor might contact them about this?
What would be your preference/expectation in this situation?