Web Forms :: Get Nested Master Page From Main Master Page

I'm trying to dynamically change the look of my main master page depending on what nested master page that the current content page is using .

So for example.

Main master page = main.master
My nested page = nested.master (uses main.master)
content page = content.aspx (uses nested.master)

So in the Page_Load event of main.master I want to add a switch statement that will check to see what nested master page is currently being used by content.aspx, or whatever content page is loaded.

So far I have got

protected void Page_Load(object sender, EventArgs e)
{
string nMaster = //This is the line of code that I am looking for.
switch(master)
{
case "nested.master":
//all my logic here.
break;
}
}