Romana III's Gallifrey

One of the many Gallifreys, was ruled by War Queen Romana III (PROSE: The Shadows of Avalon) before being destroyed by the Eighth Doctor during a Faction Paradox invasion, seemingly averting the War in Heaven and leaving him the last of the Time Lords. (PROSE: The Ancestor Cell, The Gallifrey Chronicles)

Although the account depicting its destruction described it as the original Gallifrey, (PROSE: The Ancestor Cell) other accounts called its primacy into doubt, (PROSE: Crimes Against History) even if it was notably located at the original's coordinates in the constellation of Kasterborous, (PROSE: The Ancestor Cell) One account went as far as claiming that it was a mere "sheath echo" rather than one of the main nine cloneworlds. (PROSE: The Story So Far...)

Origins
Some accounts suggested that, whatever its status within the Nine Gallifreys project, Romana's Gallifrey reflected one version of an unstable history.

According to the Book of Lies, (PROSE: Unnatural History) after President Romana's reconciliation with the Sisterhood of Karn, (PROSE: Lungbarrow) the Great Grey Eminence made a deal with Faction Paradox to undo the changes and restore his preferred order to Gallifrey (PROSE: Unnatural History) by manipulating the timeline of the newly-regenerated Eighth Doctor. (PROSE: The Eight Doctors, Unnatural History) Subsequently, the Eighth Doctor was uncertain if Romana or Flavia was President. (PROSE: Unnatural History)

The idea that this Gallifrey was the original was supported by it being located in Kasterborous, (PROSE: The Shadows of Avalon, The Ancestor Cell, The Gallifrey Chronicles) but The Book of the War speculated that the original Homeworld was moved from its original location and replaced with a copy as part of the cloneworld project. (PROSE: The Book of the War) Visions given by loas to Mother and Father by the loas claimed that the Romana III's Homeworld was only a sheath echo believing itself to be the original. (PROSE: The Story So Far...)

Another account suggested that the Lady President's ceding of the Presidency to the War King was "suggested in some quarters" on the War King's Homeworld to have been a consequence of her becoming "the head of the Presidency on one of the other Homeworlds" in order to "complete the illusion that her world [was] the original". Other rumours suggested that "even she might not realise she's been moved to a fake". (PROSE: Crimes Against History)

Path during the War
The High Council was made aware of the War through monitoring of the Obverse and the conflict in the Enclave. President Romana regenerated into a body more suitable for war (PROSE: The Shadows of Avalon) and made herself War Queen and Mistress of the Nine Gallifreys. (PROSE: The Ancestor Cell)

In preparation for Gallifrey's "darkest hour", (AUDIO: Luna Romana) Romana began stockpiling weapons in the Slaughterhouse, a secret arsenal protected by a time eddy, (PROSE: The Ancestor Cell) and she cleared whole sections of the planet to start building Battle TARDISes. (AUDIO: Luna Romana) She planned to use Bull-TARDISes to mate with Compassion to create a new Type 103 TARDIS; (PROSE: The Shadows of Avalon) unlike the War King's Homeworld, (PROSE: The Book of the War) Romana's Gallifrey was able to find and capture Compassion. (PROSE: The Shadows of Avalon, The Banquo Legacy)

Shortly before the Event and during Romana's 150th year as President, the Edifice appeared in the sky of this Gallifrey and began sending temporal waves over the planet, making its residents superstitious and agitated. This was followed by Mother Mathara's Faction Paradox invasion of Gallifrey, which resulted in the Eighth Doctor destroying the planet with the Edifice weapons. (PROSE: The Ancestor Cell)

The Tenth Doctor, thinking back to his destruction of Gallifrey at the end of the Last Great Time War, remembered the events of the Eighth Doctor's destruction of Gallifrey to stop the War in Heaven. (PROSE: The Ancestor Cell, The Eyeless)

Behind the scenes
The first edition of Crimes Against History treated the War Queen's Homeworld as the original, while the second edition had her dropping out of the narrative to be replaced by the War King, with a suggestion that she had gone on to become the President of one of the Nine Gallifreys as part of a ruse to construe one of the Cloneworlds as the original. Although this rumour can be taken at face value, a possible interpretation is that these rumours were spread by the War King himself to spread the belief that the Homeworld under his control was secretly the original despite the blatant fact of the original President — Romana — still ostensibly ruling the original Gallifrey at the original coordinates.