They ain't lose a daughter, got a son
When Beyonce married Jay-Z, as most parents fear, they didn’t lose her as a daughter to Jay-Z but rather gained him as a son.
This indicates a close relationship with her parents.
Could also be a reference to The Godfather where Michael tells the father of Apollonia that instead of losing a daughter he could gain a son
Additionally it could be a reference to how this is a wedding song (likely played at a reception) where parents often fear losing a daughter that night, but should rather realize they’re gaining a son.
This also refers to the fact that Beyonce and Jay Z took each other’s names — legally Jay Z is Sean Carter-Knowles. They did this specifically so that the Knowles line would not die out (all daughters in the family).
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