Hey there, it's not very often but every now and again I seem to run into claims that Charlemagne never existed, what is the reasoning behind this assertion and do they have any backing?
This is the Phantom Time Hypothesis.
It has been asked a few times before:
https://www.reddit.com/r/AskHistorians/comments/2mkve2/is_there_any_credibility_to_the_phantom_time/
It is generally regarded as crackpottery.