The Fab 'Parting Gift' Mansion
TMZ has learned ... Simon moved out of the home a few years ago ... when he upgraded to a spiffier 6-bedroom $12 million dream home ... just a few miles away (below).
As we previously reported, Simon felt Mezhgan "deserved" the old property for having to deal with all of the public scrutiny that comes with dating the "X Factor" honcho.
The real question -- why did Simon have an old mansion just lying around? If you have to ask, you can't afford it.