Outlook is adding attendee that wasn'tinvited

Whenever I create a new meeting an attendee that I didn't invite is being added.  This happens every time and it is the same attendee.

1.  Create meeting.

2.  Invite attendees.

3.  Send invite.

4.  If I open the meeting in my calendar, the attendee is there as a required attendee.

I can not figure out how this person is being added.