Format appearance of EXCEL spreadsheet

I recently opened a file that I had been working in and there appeared an area outside of the spreadsheet.. as per image below.. 

It appears to be associated with hiding areas of the spreadsheet..

Have no idea how or why it is there..I have searched all the ribbons to see if there was a formatting entry.. but could not find, 
If you add a sheet it is normal.. 
it is in the file as I have opened on different computers with same view

Can anyone explain.. never seen before