how to achieve an apache Alias with a proxy pass on the same domain

We have a NodeJS site running with an Apache VirtualHost that looks like this:

<VirtualHost *:80>
    ServerName      domain.org
    ServerAlias www.domain.org

    ProxyPass / http://localhost:8884/
    ProxyPassReverse / http://localhost:8884/

    ProxyPreserveHost on

    LogLevel debug
</VirtualHost>

This works fine.

however we have now been tasked with installing a wordpress blog as an alias of the domain

www.domain.org/blog

To do this we tried setting up a vhost with an Alias like this:

<VirtualHost *:80>
       Alias /blog /var/apache-vhosts/www.domain.org-blog

       <Directory /var/apache-vhosts/www.domain.org-blog/>
           Options Indexes FollowSymLinks MultiViews
           AllowOverride All
           Order allow,deny
           allow from all
       </Directory>

        ErrorLog ${APACHE_LOG_DIR}/error.log

        # Possible values include: debug, info, notice, warn, error, crit,
        # alert, emerg.
        LogLevel warn
        CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

We have the mod_alias apache module enabled but it just wont pick it up.

Has anyone else achieved this?

I have also tried including the alias without a vhost wrapping tag but still no joy :/