Why does the flag of Savoy look exactly like the 'Dannebrog', the Danish flag?

Both use the flag of the banner of the Knights Hospitaller.A theory brought forth by the Danish historian Adolf Ditlev Jørgensen in 1875 in his book "Danebroges Oprindelse" is that the Danish flag is the banner of the Knights Hospitaller. He supports his theory with that the order came to Denmark in the latter half of the 12th century and during the next centuries spread to major cities, like Odense, Viborg, Horsens, Ribe and their headquarters in Slagelse, so by the time of the Baltic crusade, the symbol was already a known symbol in Denmark.
https://en.wikipedia.org/wiki/Flag_of_Denmark