Moving a Primary Domain Controller to a different forest

Hi All,

We have a Standalone Primary Domain Controller with domain "domain1.local" in our offices.

Last year, we opened a new Branch and, in error, they also installed a Standalone Primary Domain Controller with domain "domain1.local"

We now have to join both of the domains together to create a forest with domain name "domain1.local".

According to all the google help I have come across, everyone says I have to format one of the the servers I want to move to the forest, but I do not want to format either of the servers.

If someone has some information to assist me, it would be highly appreciated.

Thank you

Ryno