How to correctly reference a supervisor who in the meantime got a doctorate I completed one of my theses under the co-supervision of a (back then) PhD student. Said person has since completed his degree and is now officially "Dr. supervisor".

Since I want to reference his supervision in my CV, I was wondering whether I use the formal title that he holds now, or whether I reference him without a PhD, which was his status during the supervision?

I am pretty sure that this is more a non-issue for my specific case, but I can see this being a more common problem elsewhere, especially when listing references online.
FYI: I did not reference the name of my supervisor advisor at all in my industry-targeting resume.  I do realize this may be different in CV-land.
I personally wouldn't use any honorifics in the CV.  (Next you'll be asking about assistant versus full professor!)  Just convey the information, the name.  I would opt for FI, LN.  I.e. Advisor: D. Linger.  Keep it tight, man.