The Watcher was introduced in the 1981 episode Logopolis. The final episode starring the Fourth Doctor ... It was the Watcher who escorted Nyssa of Traken to join the Doctor and his companions.

That in itself would make Nyssa’s story one of the most tragic for a Doctor Who companion. But then we get to “Logopolis”, the Fourth Doctor’s final adventure.

Nyssa remained in this outfit in Logopolis, and her skirt portion changed into matching velvet burgundy trousers in the second episode of Castrovalva, the beginning of the Fifth Doctor era.