Set Property of hidden base base class

Question

I have the following code:

public class Ancestor
{
    public string Property {get; protected set;}
}

public class Base : Ancestor
{
    public string Property {get; set;}
}

public class Derived : Base
{
    public Derived(string message)
    {
        //I need both properties to have the message value
    }
}

The Ancestor and Base classes are are not my code and I cannot change them.
Is there any way to set the property of the Ancestor the value of message?
Obviously simply doing something like the following won't work

Ancestor ancestor = this;
ancestor.Property = message

because the setter is protected.

Answer 1

I've found a solution that satisfies my needs. My Ancestor class derives from an interface:

public interface IAncestor
{
    string Property { get; }
}

What I did was using explicit interface declaration like so:

public class Derived : Base, IAncestor
{
    public Derived(string message)
    {
        Property = message;
        base.Property = message;
    }
    string IAncestor.Property{get { return Property; }}
}

And now the following test passes:

[TestMethod]
public void ValidatePropertyIsFullyPopulated()
{
    const string expectedMessage = "hello!";
    var derived = new Derived(expectedMessage);
    Base baseClass = derived;
    IAncestor ancestor = derived;
    Assert.AreEqual(expectedMessage, derived.Property);
    Assert.AreEqual(expectedMessage, baseClass.Property);
    Assert.AreEqual(expectedMessage, ancestor.Property);

    //Notice that this Assert WILL fail because Ancestor.Property is
    //not marked as virtual.
    Ancestor ancestorClass = derived;
    //Assert.AreEqual(expectedMessage, ancestorClass.Property);
}