Venus

Venus is a planet in our solar system that lights up in the night sky, which itself is named after a goddess from ancient mythology. And not just any goddess, but the goddess of love.

Fabrizio sees both the star and the goddess when he looks out at the night sky. Appearing as both a faraway star and an unobtainable (and super-hot) goddess, Venus represents all of the satisfaction that the Prince thinks he'll never be able to achieve in his life. At the same time, though, he thinks of this woman-star as being faithful to him, thinking,

There was Venus, wrapped in her turban of autumn mist. She was always faithful, always waiting for Don Fabrizio on his early morning outings, as Donnafugata before a shoot, now after a ball. (6.75)

It's only at the moment of his death that Prince Fabrizio comes face to face with Venus. Chances are that her appearance at his bedside is actually a hallucination brought on by a stroke, but that doesn't really matter.

As he drifts into death, Fabrizio sees Venus at his bed and thinks,

It was she, the creature forever yearned for, coming to fetch him; strange that one so young should yield to him; the time for the train's departure must be very close. When she was face to face with him she raised her veil, and there, modest, but ready to be possessed, she looked lovelier than she ever had when glimpsed in stellar space. (7.28)

The appearance of Venus means that Fabrizio has finally found the sense of calm acceptance he's always wanted out of life. Turns out though that this acceptance can only happen at the moment of his death, since it's pretty hard to keep worrying once you're dead… and super easy to keep worrying the whole time you're alive and kicking.