It depends on various things such as where you are in Spain as some provinces have different rules, how the will is wrote, if the property is in both your names etc
In general you would have an allowance of around 16,000 Euros, you then pay a % of the remainder
So if for instance you say 50k of property is yours and 50k your partner then an allowance would bring it down to about 34k, on that you would pay 11.05% yours, being about 3700 Euros in tax.
Of course other things will come into it and I’m no doubt other forum members will have a say.
Ian