Amazing. We have 3 or 4 here, plus the arrival of the house martins a week or two ago.
I was wondering if your solitary swallow will be waiting for its partner to arrive and whether it will find another if he/she doesn't arrive. Here's an article on it: https://www.avcr.cz/en/news-archive/...%20is%20common.
Like a lot of small birds, there's plenty of scandal in swallow love lives.