The following code example pulls out the last 5 published WordPress posts by their ID, extracts the first ID (which is the last published post ID) and then extracts the post’s tags into an array.
$return_tag_array is a list of the last published post’s tags.
//Get list of past published posts, up to 5
$args = array(
'numberposts' => 5,
'offset' => 0,
'category' => 0,
'orderby' => 'post_date',
'order' => 'DESC',
'include' => '',
'exclude' => '',
'meta_key' => '',
'meta_value' =>'',
'post_type' => 'post',
'post_status' => 'publish',
'suppress_filters' => true
);
$published_posts = wp_get_recent_posts( $args, ARRAY_A );
//Pull off the top most post, & retrieve the ID
$last_published_post = reset($published_posts);
$last_published_post_id = $last_published_post["ID"];
//TAGS
//Use the post ID to pull off tags
$tags = wp_get_post_tags($last_published_post_id);
$return_tag_array = array();
foreach ($tags as $tag) {
$tag_name = $tag->name;
array_push($return_tag_array, $tag_name);
}