How to get specified parent page title in my function

Question

Below I have a function that prints the child pages of a parent. I am trying to obtain the specified parent pages title as a h2 above the unordered list.

I have tried updating the title_li and also the final returned result but cannot work out what what I should be putting in there. What function can I use in one of these places to get the desired result? Thanks!

function childpages_shortcode_callback( $atts ) {
    $atts = shortcode_atts( array(
        'parent' => false,
    ), $atts, 'childpages' );

    $parent_id = false;
    if ( $atts['parent'] ) {
        $parent = get_page_by_path( $atts['parent'] ); 
        if ( $parent ) {
            $parent_id = $parent->ID;
        }
    } else { // if no parent passed, then show children of current page
        $parent_id = get_the_ID();
    }

    $result = '';
    if ( ! $parent_id ) {  // don't waste time getting pages, if we couldn't get parent page
         return $result;
    }

    $childpages = wp_list_pages( array(
        'sort_column' => 'menu_order',
        'title_li' => '',
        'child_of' => $parent_id,
        'echo' => 0
    ) );

    if ( $childpages ) {
        $result = 
            '<h2>' . 'Parent title here' . '</h2>' . 
            '<ul>' . $childpages . '</ul>';
    }

    return $result;
}
add_shortcode( 'childpages', 'childpages_shortcode_callback' );

Answer 1

Use get_the_title

Replace the last part of code

if ( $childpages ) {
        $result = 
            '<h2>' . 'Parent title here' . '</h2>' . 
            '<ul>' . $childpages . '</ul>';
    }

with

if ( $childpages ) {
        $result = 
            '<h2>' . get_the_title( $parent_id ) . '</h2>' . 
            '<ul>' . $childpages . '</ul>';
    }

This may also help.