It is speculated that this object may well be a "brown dwarf" - a failed Star. Many stars have been noted to be "binary systems" - twin Suns - whereas our solar system only has the one. The most likely explanation is that this object started out as a star, but lacked the necessary mass to continue, and eventually fizzled out, eventually orbiting around our Sun in a very large elliptical orbit of 3600 years or so.
Montalk does not specifically name it in his document, but he did a "mathematical analysis of the data provided by the
Cassiopaea session transcripts on the subject of the twin sun and associated effects":
For a while I have been researching the Planet X idea and its many variants, from the theories of Sitchin to Zetatalk, Barry Warmkessel, Richard Muller, and Velikovsky. And of course the version explored in the Cassiopaean transmissions which are close to Richard Muller’s theory of a dark star companion that swings by every 26-27 million years. The twist is that via its highly elliptical orbit, it punches through the Oort cloud and sends a trailing cluster of comets into the solar system which then establish a 3600 year orbital cycle, periodically pelting the inner solar system.
(See the PDF there.) Am sharing this because I found it very informative.