If a distribution was made from your IRA and was given to your ex, you are the one responsible for this income, reportable on your tax return. The only way to transfer part of your IRA to your ex without it being a distribution paid to you and subsequently given to your ex is for a portion of you IRA to be transferred trustee-to-trustee incident to divorce to an IRA in your ex's name. A trustee-to-trustee transfer is not a reportable transfer and no Form 1099-R would be issued by your IRA trustee for a trustee-to-trustee transfer.