Who are you???

A’ ‘new’ cat appeared in our garden today. She ( I think it’s a female) followed Mia under the back fence , then was transfixed by the birds in our trees. At first I thought it was the cat we have named “young Taz’, but no, this one has a large white patch on its chest. No collar though. I wish people would collar their cats. I don’t want to encourage other people’s cats, but it would be useful to know if it were a stray needing cared for. I think she looks in great health so she musthave a home.