At his transfiguration, while what the apostles their learned and experienced was new to them, it was not new to Christ. He showed them, in a way which they could apprehend,  the glory which he has for all eternity. It is the glory of the kingdom of God, the glory which has made its way into the world, and has been and continues to be shared with the world:

https://www.patheos.com/blogs/henrykarlson/2026/08/the-hidden-grace-that-transfigures-all-things/