How to get foreign table if there are two foreign key to same table?

This is the Model, and I want get both user's data

    class PersonalMessage extends BaseModel
    {

        public $fromUserId;
        public $toUserId;

        public function initialize()
        {
            $this->belongsTo('fromUserId', 'User', 'id', array('foreignKey' => true));
            $this->belongsTo('toUserId', 'User', 'id', array('foreignKey' => true));
        }
    }

and I use this to get user

    {{personalMessage.user.username}}

But I can only get the data which linked to toUserId

How can I get the other user?