Let Bygones Be Bygones

A "bygone" is something which has already happened; the time when it happened has "gone by". We say "let bygones be bygones" to people who have had a disagreement in the past when we want them to move forward leaving their disagreement in the past. Example: "You and I have had our disagreements; let's let bygones be bygones." {often used with: Forgive and forget}