Laravel - 5.8 one to many relation returns null

I have Cars model which belongs to two other models Region, Subregion. Cars Model:

function region(){
    return $this->belongsTo('App\Models\Region');
}
function subRegion(){
    return $this->belongsTo('App\Models\Subregion');
}

Subregion model:

class Subregion extends Model{

public $timestamps = false;

protected $fillable = [
    'name'
];

public function cars(){
    return $this->hasMany('App\Models\Car');
  }
}

Region:

class Region extends Model{

public $timestamps = false;
protected $fillable = [
    'name'
];

public function cars(){
    return $this->hasMany('App\Models\Car');
  }
}

I have query which selects Cars with their region and subregion:

$queryCar= Car::with(array(
        'region'=>function($query){
            $query->select(['id', 'name']);
        },
        'subregion'=>function($query){
            $query->select(['id', 'name']);
        }
))->orderBy('id', 'DESC');

return $queryCar->get();

Table cars has columns region_id, subregion_id.

When I try to loop the cars result:

    foreach ($cars as $p){
        var_dump($p->subregion);
        var_dump($p->region);
    break;
    }

For the region, I see the result, which is not NULL, but there is no subregion. I am sure that there is, because, if I do:

var_dump($p);

I can see and subregion_id and if I query database with that id, there is a subregion row.

It is strange, because everything is equal for these two - Subregion/Region.

via Chebli Mohamed