Actually I just got it!

Dim ms As MatchCollection = Regex.Matches(_TreeNode.Parent.ValuePath.ToUpper, "[A-Z0-9]{8}-[A-Z0-9]{4}-[A-Z0-9]{4}-[A-Z0-9]{4}-[A-Z0-9]{12}")
Me.ParentGUID = ms.Item(ms.Count - 1).Value.ToLower '--Get the last item, it is the parent guid.