I”m just ACF, and i’ve created and Image as an ID. The code is all working perfectly apart from the alt tag isn’t being outputted.

What have I got wrong?

<?php 
$attachment_id_desktop = get_sub_field('image');
$size_desktop = "column-size"; // (thumbnail, medium, large, full or custom size)
$image_desktop = wp_get_attachment_image_src( $attachment_id_desktop, $size_desktop );
$alt_desktop = get_post_meta($attachment_id_desktop , '_wp_attachment_image_alt', true);
?>

<img class="img-fluid desktop" alt="" src="<?php echo $image_desktop[0]; ?>" alt="<?php echo $alt_desktop; ?>"/>