How do you add an index field to Linq results

Lets say I have an array like this:

string [] Filelist = ...
 

I want to create an Linq result where each entry has it's position in the array like this:

var list = from f in Filelist
     select new { Index = (something), Filename = f};
 

Index to be 0 for the 1st item, 1 for the 2nd, etc.

What should I use for the expression Index= ?

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