Leave it Buried
Sometimes, certain events unfold in such a way that no consensus or discussion is necessary – everyone involved instinctively understands the need for secrecy. The OP and their father-in-law shared an unspoken understanding that this secret would remain buried with them, an unspoken pact binding them as family.
There's an undeniable truth that some incidents defy time and distance – they remain etched in memory, unalterable by the passage of years. Such is the case with this incident, destined to be consigned to the deepest recesses of their souls.
