US inheritance tax for Spanish tax resident

The US estate tax (if any) is paid by the estate, not by the beneficiary, and what the beneficiary gets is whatever is left after the executor of the estate pays the estate tax. In some cases, the executor may be forced to sell some of the assets to pay the estate tax, and so the beneficiary gets what is left. For example, the will of the deceased might have left all the shares of Apple stock that the deceased owned to the OP, but the executor might be forced to sell off some of that stock because there is not enough cash to pay the estate tax. Regardless, whatever the beneficiary receives is not taxable US income to the beneficiary. How Spain regards such transactions is something I don't know. If there is a tax treaty between the US and Spain, such tax treaties typically say that transactions in each country are taxed by that country alone, and if there is any income tax due in one country on income in the other (for example, the US taxes its citizens on global income), then that country will give a tax credit for the income tax paid to the other country; the US gives such tax credits even in the absence of a tax treaty. Unless the deceased (US citizen) was also a resident of Spain and his estate was probated in Spain, I don't think that Spanish inheritance tax would be due, but I am not a tax professional....