You can use this:
$array = array("one" => "apple", "two" => "orange", "three" => "pear");
end($array);
echo key($array);
Another Solution is to create a function and use it:
function endKey($array){
end($array);
return key($array);
}
$array = array("one" => "apple", "two" => "orange", "three" => "pear");
echo endKey($array);