How to disable tinyMCE button added by a plugin?

I know how to disable TinyMCE default buttons with add_filter('tiny_mce_before_init') using theme_advanced_disable parameter, but a button added by a 3rd party plugin seems impossible to hide with tiny_mce_before_init

The available array with add_filter('mce_buttons') returns only the default tinyMCE buttons.

How to disable this tinyMCE button?

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I’ve found that you can manual set availability button by this attribute theme_advanced_buttons1 (for button in row 1)

Example :

function disable_mce_buttons( $opt ) {
    //set button that will be show in row 1
    $opt['theme_advanced_buttons1'] = 'bold,italic,strikethrough,|,bullist,numlist,blockquote,|,justifyleft,justifycenter,justifyright,|,link,unlink,wp_more,|,spellchecker,wp_fullscreen,wp_adv,separator';
    return $opt;

add_filter('tiny_mce_before_init', 'disable_mce_buttons');