It looks a lot like the hardy begonia (B. grandis) I don't know what zone they are not hardy but they grow well in the Atlanta area. I've had mine in metal pans for the last 3 or 4 years and they always come back plus some new ones (from bulbils at the nodes or seed).

seed capsules and stems back in late Feb.

Five days ago. It shares the same pan with two different types of florist ivy.

Blooms late August last year.

You kind of see the red nodes on the stems.
July 25, 2020 showing two different colors of the leaves. It's like one part of the pan has different soil than the rest of the pan.

There is a good resemblance, except the flowers don't look anything like what I had last year. The blossoms are just forming now -

It could be a cultivar of hardy begonia or at least a hybrid of it. Too many similarities to dismiss. The node color for example plus that it goes dormant for winter no matter how much you try to keep it going through its genetic nature.

Look at Heron's Pirouette as an example.

It does look like it! The blooms will tell the story I suppose.

I don't really recall having this type of begonia last year - I thought I had saved a non-stop (rose form) type! but as it was in a mixed basket, I am sure that I just forgot what it was after it was dormant.

Looks like it could possible be hardy in ground here (most years, anyway.) I may try to separate out one of the young sprouts and plant it out.

Thanks for your information and identification!