Okul

Okul was the home planet of the Frovians, a time-travelling species who had diplomatic contacts with the Time Lords and were ruled by Prince Luj.

The Doctor met Luj at least twice before their final encounter, as Luj was familiar with two distinct regenerations of the Doctor. At least one of these meetings must have taken place on Okul, as the Seventh Doctor remembered Luj showing him a secret passageway in his palace.

When the Frovians prepared to sign a treaty with the Kollian Dimension that would sync its timelines with their own universe's, allowing easy travel between the two, the diplomatic meeting meant to culminate in the signing of the treaty was organised in the royal palace on Okul. The Doctor was invited as the representative of Gallifrey. However, the Seventh Doctor's TARDIS was highjacked before his arrival by Kasgi, an assassin who stole his identity, posing as the Doctor's newest regeneration. She had discovered that Luj was actually a bloodthirsty conqueror, who had deceived the real Doctor along with everyone else. The Seventh Doctor managed to escape and find a non-lethal way to prevent the signing of the Kollian treaty, however. He then departed in his TARDIS, with Kasgi watching him from afar, reflecting on the difference in their methods. (COMIC: Who's That Girl!)