AdminBundle/Service/YoutubeService.php
public function getRelatedVideos($videoId)
    {
        $listResponse = $this->search->listSearch('snippet', array('relatedToVideoId' => $videoId, 'type' => 'video'));
        if (empty($listResponse)) {
            throw new \RuntimeException(sprintf('Could not find video with id %s', $videoId));
        }

        return $listResponse;
    }
public function getRelatedVideos($videoId)
    {
        $listResponse = $this->search->listSearch('snippet', array('relatedToVideoId' => $videoId, 'type' => 'video'));
        if (empty($listResponse)) {
            throw new \RuntimeException(sprintf('Could not find video with id %s', $videoId));
        }

        return $listResponse;
    }
Get related videos
See https://developers.google.com/youtube/v3/docs/search/list#response for returned value

@param  string $videoId
@return array