Duplicated results for non-existent alias

I have started to get duplicated results in graphs for alias that do not exist in the prometheus.yml file. The alias circled in the attached screenshot does not exists and yet is showing as a duplicate result. Other than the prometheus.yml file I am unaware of where an alias might reside to try and resolve this issue.

For anyone encountering this same issue, I have now resolved this by the following:

The duplicate data was due to the old alias still been in the Prometheus TSDB (my retention period was set to 15 days). So I enabled the admin api and manually deleted the entry in TSDB.
curl -X POST -g ‘http://localhost:9090/api/v1/admin/tsdb/delete_series?match[]={alias=“mysql1”}