What? (conflicting info) 

The shortest reign is believed to be that of Luis Filipe of Portugal who was assassinated at the same time as his father on 1 February 1908. He could thus be claimed to have been King of Portugal for 20 minutes.[1] However the Portuguese monarchy lacked automatic succession and so any claim that he was de facto king does not hold up to scrutiny.

This appears to be a case where someone has corrected something without realising how dumb it ends up sounding. If I'm reading it correctly it's saying... Luis Filipe was the shortest serving head of state. Actually we kid, he was never the head of state so he can't have been the shortest serving. The article then gives no hint as to who was the shortest serving head of state who actually served.