Based on Assimilitation 2 : Star Trek- Doctor Who crossover graphic novel.

When the Borg broke through to another dimension that also contained a Cybernetic species they were unprepared and found that they themselves were the ones to be "Assimiliated"! The Cybermen of Mondas/Telos , being even more mechanical and less emotional than the Borg, had no problem in upgrading or deleting their opponents!
Under the principle that the enemy of my enemy is my friend, the CyberBorg conquered The Federation, and the Borg Queen was reunited with her Locutus.