I can't get a simple id

[eluser]Sein Kraft[/eluser]
I cant get the last added id (is an autoincrement id in sql) to use in other table.
Model:

Code:

function id()
    {
        $query = $this->db
        ->select('id')
        ->from('imageboard_image')
        ->limit(1)
        ->order_by('id','desc');
        
        return $query;
    }

Error:

A PHP Error was encountered

Severity: 4096

Message: Object of class CI_DB_mysql_driver could not be converted to string

Filename: libraries/Parser.php

Line Number: 63