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Gayngst for a more general idea, The Pastor's Queer Kid is related but more specific.
I do some cleanup and then I enjoy shows you probably think are cringe.It would only be Dramatic Irony if he does not know about his kids being LGBTQ but we as the audience do.
There is also some Cosmic Irony in the situation of a vocal homophobe having multiple LGBTQ children, especially if it hits "statistically improbable" levels (see the "Types of Irony" section on the irony page)
Is there a specific trope for someone that is explicitly homophobic and mostly of his kids are LGBTQ? Could Dramatic Irony fit in this situation?