Featured post showing twice

Snippet of code from https://www.sonnygill.com that may help make more sense:

<div id="featured">
	<div class="wrapper clear">
		<?php $lastposts = get_posts('numberposts=1&category=18');
		foreach($lastposts as $post) :
		setup_postdata($post); ?>
		<div class="left"><img src="<?php echo get_post_meta($post->ID, "featured", true); ?>" alt="" /></div>
		<div class="right">
			<h1><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h1><span><?php the_time('dMy'); ?></span>
			<?php the_content(); ?>
			<p class="right"><a href="<?php the_permalink(); ?>">continue reading</a></p>
		<?php endforeach; ?>
		</div>
	</div>
</div>

Have a look at this. You’ll need to add a check for the featured post id in the second loop.
https://codex.www.ads-software.com/The_Loop#Multiple_Loops_in_Action

I’m still having a difficult time understanding which code to implement.

I’ve implemented this bit of code <?php query_posts($query_string."&order=DESC&cat=-18"); while(have_posts()) : the_post(); ?> into where the current query is located below:

<div class="content">
		<?php query_posts('cat=-18&orderby=ID'); ?>
		<?php query_posts($query_string."&order=DESC"); while(have_posts()) : the_post(); ?>
			<div class="post">
				<h1><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a><span><?php the_time('dMy'); ?></span></h1>
				<?php the_content(); ?>
				<div class="meta">
					<span class="left"><?php comments_popup_link('no comments', '1 comment', '% comments'); ?></span>
					<span class="right">filed under <?php the_category(', '); ?></span>
				</div>

What it does is get rid of the featured post showing twice BUT post order is reverted back to ascending. I have to put the DESC query because my posts are shown in ascending order otherwise.