How do I get rid of a second window in Excel?

[AlphaDog]

I opened a second window this morning to cross check entries, and now I can't get rid of the extra! I've done this before many times and usually it simply disappears when I close it, but this time the silly thing won't go away. Help! Might I have accidentally hit Save when I was working on the duplicate? I can't find a second copy of the workbook in my folder, but two identical workbooks open every time I try to access the original. Any help in getting rid of this creepy thing will be appreciated! Thank you.