Preparing a will ,

Dear sirs

I am 45 years old and wish to make my will

My case is such apart from my own house and bank accounts, I am likely to be willed a certain part of my issueless sister's property 

I have been taking care of my sister since 15 years old and she has expressed desire to leave me an immovable property after her death.

How do I mention the above part in my will because it has not yet come in my name

regards

Jessie