Class 'App\Http\Controllers\Admin\Controller' not found

Why am I getting Class 'App\Http\Controllers\Admin\Controller' not found on in AdminController.php line 9?

I have looked at my routes and namespaces and they look ok.

Routes:

<?php

/*
|--------------------------------------------------------------------------
| Routes File
|--------------------------------------------------------------------------
|
| Here is where you will register all of the routes in an application.
| It's a breeze. Simply tell Laravel the URIs it should respond to
| and give it the controller to call when that URI is requested.
|
*/

Route::get('/', function () {
    return view('welcome');
});

/*
|--------------------------------------------------------------------------
| Admin Routes
|--------------------------------------------------------------------------
|Controls all of the routes that make the admin area work
*/

Route::group(['namespace' => 'Admin', 'prefix' => 'admin'], function() {

    Route::get('admin','Admin\AdminController@index');


    Route::post('/admin/login', 'Admin\AuthController@postLogin');
});
/*
|--------------------------------------------------------------------------
| Application Routes
|--------------------------------------------------------------------------
|
| This route group applies the "web" middleware group to every route
| it contains. The "web" middleware group is defined in your HTTP
| kernel and includes session state, CSRF protection, and more.
|
*/

Route::group(['middleware' => ['web']], function () {
    //
});

Route::group(['middleware' => 'web'], function () {
    Route::auth();

    Route::get('/admin/dashboard', 'HomeController@index');
});

/*
|--------------------------------------------------------------------------
| Admin Middleware Routes
|--------------------------------------------------------------------------
|Controls all of the routes that make the admin area work
*/

Route::group(['middleware' => 'web'], function (){
    Route::auth();

    Route::get('/admin','Admin\AdminController@index');

});

AdminController:

<?php

namespace App\Http\Controllers\Admin;

use App\Http\Requests;
use Illuminate\Http\Request;

class AdminController extends Controller
{
    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct()
    {
        $this->middleware('auth');
    }

    /**
     * Show the Admin Login Page.
     *
     * @return \Illuminate\Http\Response
     */
    public function index()
    {
        return view('admin.login');
    }

    
}