Query posts distinct authors

I am trying to get post from a category ordered random, but making sure that the author does not repeat itself.

So I have this query which works as intended, but there is the chance that the author will repeat in those 4 posts. So any ideas how I could make sure it doesn't?

I was thinking of using $wpdb but I was hoping for a more straight forward solution.

$args = array (
'post_type'              => 'post',
'post_status'            => 'publish',
'category_name'          => 'premium',
'orderby'                => 'rand',
'posts_per_page'         => 4,
'post__not_in'           => get_option( 'sticky_posts' ),
'date_query'             => array(
    array(
         array(
                'before' => 'this week'
        ) 
    ),
),
);
$query = new WP_Query( $args );