Let bygones be bygones is used to tell someone that they should forget about unpleasant things that happened in the past, and especially to forgive and forget something bad that someone has done to them.

Note: It can be synonyms to ‘it’s water over the bridge.‘ But ‘let bygones be bygones encourages the desire to forgive and forget, not holding a grudge.

Why can’t you let bygones be bygones and put it all behind you?

My mother thinks I should let bygones be bygones, but I’m struggling with it.

After all these years, surely it’s time to let bygones be bygones.

If she’s willing, I’m willing to let bygones be bygones, too.

Just let bygones be bygones and be friends again. Our fight is water over the bridge. It’s about time we overcame this.

There’s no point in bearing a grudge- you have to let bygones be bygones.

Tradução: deixar o passado pra lá e fazer as pazes, perdoar e esquecer o que passou, não guardar rancores.