Altering a DATE in a cell

I have a cell that is automatically updated to the first of every month, so

=DATE(2015,8,1)

.
In another cell, I want a formula to take the year of this date and put it at December 1, 20**.
So this year =DATE(2015,12,1)
and then next year, when my first date cell goes to =DATE(2016,1,1) I want this other cell to automatically go to =DATE(2016,12,1).

In essence I need a formula to extract the last month of the year from the original date cell.

I hope this makes sense...

Thanks Chem.