Unwanted guest

My only photo today and not particularly good. I went to my son’s house early this morning as it’s my school run day for his children. Made them breakfast and played before our 5 minute warning to get organised for leaving. My grandson went to put a toy away (shock!) and said that there was a white cat on the window seat. It’s not theirs! I messaged my son as they have a neighbour’s cat who comes in regularly too, he asked for a photo and suggested I ask it to leave. It took no notice. It left of its own accord at some point.