12" will not fit.  I just measured it.  The length of the case from one side to the other side of the case is 11."  That would leave 0" for airflow between the top and bottom of the case.   If you removed the front fan, that would get you an extra 2.5 cm, but then you'd have no front fan either.  Also, you need to keep in mind the card width needs to be under 4.25" for the case to be able to close. 
I have a 12" 2080 Ti and I'm looking to get a new computer. Will this fit in either the Aurora R8 or Aurora R9? Thanks
Aurora R8/R9, graphic card max length?