Charles Rennie Mackintosh was one of the must under-rated and unappreciated architects of the twentieth century. He didn't build much, nothing outside of his native Scotland, and was pretty much forgotten about everywhere else. He was rediscovered in the sixties by academic Thomas Howarth and other authors who disagreed with Howarth, but all came to realize that he was a genius at architecture, interiors and furniture design.
His masterpiece was the Glasgow School of Art, which was pretty much destroyed by fire today. A projector in the basement exploded and the fire spread right up to the roof. The building has a steel frame and stone walls so part of it may well be saved, but a highlight, the library, is probably gone.
I do go on about how the greenest building is the one already standing, and about how much we can learn from them, how they are not relics from the past but templates for the future.
In this case, I can only say that one of the world's great buildings has been lost, and it's tragic.