If DFAS reported it to you on a Form 1099-R, it may not be "your" retirement, but you will have to report it in the 1099-R interview of Retirement income and Social Security.
It won't be taxed any differently than spousal support (alimony), but the IRS got a copy of the 1099-R from DFAS and will want to see it reported (as a 1099-R) on your tax return.
