Calendar Invitee - Random Address

Hi - when I wish to add an invitee to a new calendar appointment in my iPhone Calendar App, and I click the arrow in the Invitee field (which has a default of 'none') then as well as having the choice of adding my partner - we have shared our gmail calendars - there is now also a random email address from someone at work...and she isn't even a contact on my phone! Or a Google contact. Does anyone know why this might have happened and where the App is pulling the email addresses from? And how do I remove this person as a proposed invitee? Hard pressing her email address does not give me the option to delete or remove her. Many thanks - S.