There have been times in my career when I have performed in the so-called ‘modern premiere’ of a work, but I think performing in an actual premiere of a work that was written in the eighteenth century but never performed at the time is a first for me. 

‘Composed in 1788, Salieri’s opera Cublai, Gran Kan De’ Tartari was a satire on the autocracy and court intrigues at the court of the Russian Tsarina, Catherine the Great, but was abandoned before its scheduled premiere as the theme became too sensitive when Austria entered the Russo-Turkish conflict.’
https://www.classical-music.uk/news/article/opera-to-premiere-235-years-after-composition

The work in question was the Italian version of Antonio Salieri’s Cublai gran kan de' Tartari (1788), which I performed as part of a residency at the Theater an der Wien, Halle E (in Vienna’s Museumsquartier) with Christophe Rousset and Les Talens Lyriques, and an excellent cast comprising: Carlo Lepore (Cublai), Alasdair Kent (Timur), Marie Lys (Alzima), Äneas Humm (Posega), Fabio Capitanucci (Orcano), Giorgio Canduro (Bozzone), Ana Quintans (Memma), Lauranne Oliva (Lipi) and Christoph Wagner-Trenkwitz (in the spoken role of Salieri). The Arnold Schoenberg Chor formed the ensemble for this elaborately staged opera, complete with dancing Mozart-style kügels, a revolving stage, a live dog (namely Marie Lys's dog, Loïsi), and a catwalk around the perimeter of the pit—I mean, what could possibly have gone wrong! (To answer that question, fortunately nothing much, apart from a picture frame prop falling apart in Cublai's hands in one of the shows!) Christophe appeared wearing a false beard in the last show (there is a pivotal scene in the opera where all the men shave off their beards)!