<?php

$tests = [
    "Apelido\n\nFulano de Tal",
    "Apelido:\nFulano de Tal",
    "Apelido: Fulano de Tal"
];

foreach($tests as $test) {
    
    if (preg_match("/(Apelido\:?)(\s+)(.*)/", $test, $matches)) {

        echo $matches[3], PHP_EOL;
        
    }
    
}