XML : How do I put distinct values from a LINQ query into a list?

I've looked at several answers to similar questions, but none of them solve my problem. All I need to do is get distinct values from a LINQ query (that queries a XML file) and put them into a list. Here is what I have tried:

   var XmlData = XDocument.Load("PathToFile");      List<string> XmlItems = new List<string>();        var XQuery = from m in XmlData.Root.Elements()                   where m.Attribute("Category").Value.ToString().Equals("TheCategory")                   select (m.Attribute("TheAttribute").Value).Distinct().ToString();        XmlItems.AddRange(XQuery);        foreach (var item in XmlItems)      {          ComboBoxTeams.Items.Add(item);      }    

The Distinct() function call is not working. I'm unfamiliar with how to get distinct values from a LINQ query. Any suggestions?