this is a reference to 'SE03E13 - Screwed the Pooch': peter proves that brian is a caring family member by showing that he knows the most intimate family secrets - even 'the name of megs real father' which is 'Stan Thompson' (skip to ~0:19:50). meg doesn't seem to know about this.

Could Lois have been with Stan Thompson before marrying Peter? Meg is the oldest, so it would make sense if Meg was born with Stan, then Lois married Peter soon after.

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