Select distinct values in all nested collections using LINQ to objects?

Given the following code setup:

public class Foo {
 List<string> MyStrings { get; set; }
}

List<Foo> foos = GetListOfFoosFromSomewhere();

How do I get a list of all of the distinct strings in MyStrings across all of the Foo instances using LINQ? I feel like this should be easy, but can't quite figure it out.

string[] distinctMyStrings = ?