I went out to the car yesterday and found I had a flat front tyre ....... took the wheel off and replaced with spare - (which was also flat

After a closer inspection of the flat I found this as attached. Now I have never had an alloy crack but I was a bit surprised at this - has anyone else seen or experienced something similar with an 18" Avus ??
Also just in case someone happens to stumble across this thread before I put up a for wanted post, I need one 18" avus with tyre please !!
Dan