I am sure that the answer that is required is Charles the First, but in actual fact Charles the Bald was Charles the Second!
https://www.britannica.com/biography/Charles-II-Holy-Roman-emperor
https://en.wikipedia.org/wiki/Charles_of_France
In French kings Charlemagne was counted as Charles the First
....Kings of the Franks or of France
Charlemagne (c. 742–814), counted as Charles I, reigned 768–814
Charles the Bald (823–877), counted as Charles II, reigned 840–877
Charles the Simple (879–929), counted as Charles III, reigned 893–922
........