Running into an ex… dog.

In cases of rehoming, how long would a dog recognize a previous owner after living with a new family? Or another example: if a couple splits up and one person moves out, would the dog recognize them if they saw them years later?

I just imagine a dog seeing someone who used to be a big part of their life and being sad, and then it makes me sad.

*Not rehoming my dog. He’s stuck with me.