Cape, Chapel, Chapeau

We can sometimes get a clue when a word came into English from the French by its pronunciation.  French changed over time, the same as English or any other language, and different regions had different dialects. Cape, and cap, may have come from either Germanic or directly from Late Latin, and had that hard - k sound. It had that sound in Old French, too. But that sound softened under the Normans to a ch- .  Those Northmen had dropped their Old Norse within a few decades after arrival in Normandy, but their French was accented differently than those in Anjou or Paris. Chapel has an interesting story of deriving from a cloak that St Martin tore in half to give to a beggar, and saw in a dream that night that the beggar was actually Christ.  The remaining half-cape became a relic, and the places put up to protect it (it was moved a few times) were called chapels.  It came in with that pronunciation in the 11th C.  Chapeau is not English but is a highly-recognisable French word that was not Norman, but more standard dialect and came to us much later.  It has the sh- sound.

We hear those same sounds in  Karolis (Magnus), Charles le Magne, and then Charlemagne.  The gentleman in question spoke a Frankish dialect and pronounced his name with the k- sound, and that would have been the sound in Anglo-Saxon English and Danish as well, until the Norman Conquest.  But they had softened it to the ch- sound and "Charles" became a common name in England for centuries.  In the meantime, the pronunciation of ch- was changing in the rest of France, and his name eventually started with an sh- sound, as now. If you traveled to 800 AD and asked for Charlemagne, no one would know who you were talking about.