When Michael Corleone dies at the end of The Godfather Part III, he is sitting almost exactly where he was standing when Apollonia was killed in the first film.
Apollonia dies about 2 hours into the first film and we don’t really hear her mentioned ever again in the trilogy until an hour and a half into the third film when Michael has his flashback as he contemplates the Mary/Vincent relationship. They spent the entire second half of Part III reminding us about Apollonia- the woman who accidentally died in Michael’s place- and tying her in to Mary’s storyline in order to prepare us for when Mary will accidentally die in Michael’s place.
After Mary is killed, we get the montage of Michael dancing with the 3 women: Mary, then Apollonia, and finally Kay. The cut from Michael dancing with Mary to the clip from the first film of him dancing with Apollonia at their wedding brings the whole thing home. But putting him just a few feet from where he watched Apollonia die for his own death, that complete the full circle of this whole violent tragedy.