Assume that, in a modern kingdom, the Crown Prince murders the king. He technically becomes king, as he's the legal heir of the throne. Could the prince be prosecuted for that and denied the throne?
In 1648, the Parliamentarians were debating the charges to try Charles I for, and one of those that came up was a claim that he killed his father James. Would these kinds of cases mean that you could prosecute them on the grounds that they were not legitimately made king and this doesn't have sovereign immunity?
Edit: Not specific to a particular country. Nepal had a famous regicide in 2001. Also, the Kuwaiti Sheik just died. If that was caused by his brother who is now the Sheik shooting him for instance, that would also count.