We start with the frame with the Inca.
Take away the colours to see the lineart clearly.
Superimpose it over the Bellini painting, I have dimmed the colours a bit for clarity, and you can clearly see the likeness. Notice how the profile, cheek bones, eyes, mouth and even the dimples match. I don't think this is a coincidence, rather an intelligent loan by Hergé.
Here are the two side by side. Bellini is one of my favourite painters, this painting especially. I definitely saw Hergés version first so I wonder if that has something to do with me appreciating the Doge painting.
In my opinion this doesn't deteriorate Hergés work in any way. I see it as a homage to Bellini and as T.S. Eliot said: 'Bad writers imitate, good writers steal'.