Ask HN: Ever found your job is being advertised?

One of my directs showed me a job advert for a VP of Engineering and asked if my boss had resigned. There is no doubt that the advert is for our company and it’s the first my boss had heard about the advertised position. He suspects his boss and some of the other managers are trying to get rid of him. Is this kind of secret conspiracy common? It’s also possible that I will be demoted back to an individual contributor role and my boss will report to the new VP. Anyone had this happen to them?