How can I remove duplicate characters in a string?

So I have $comment but they decided to say "aaaaaaaaaaaaaa" or any other string of characters that is repeated more than 3 times.

How do I remove those words from the string?

It would be ideal to check if any characters are repeated more than 3 times and replace those characters with a blank space, or something like that

Any ideas?

 

preg_replace can probably do it, but i have no clue about what reg exp is needed for this. sorry.

 

Yes I figured as much, but I'm useless with regex.

 

$string = 'aabbccaaaaaddee';
$new_string = '';
$starting_char = 0;
while (strlen($string) > 0 && $starting_char < strlen($string)) {
    $blah = preg_match('/[A-z]{3,}/', $string, $matches);
    $letter = $matches[0][$starting_char];
    $new_string .= $letter;
    $regex = '/' . $letter . '{3,}/';
    $string = preg_replace($regex, $letter, $string);
    $starting_char++;
}
echo $new_string;

PHP: