This extraordinary photograph appeared on Twitter a few days after the death of the Queen. It shows nine Kings at the funeral of Edward the VII in 1910.
In the back row from left to right:
Haakon VII of Norway, Ferdinand of Bulgaria, Manuel II of Portugal, Wilhelm II of Germany, George the I of Greece and Albert I of Belgium.
In the front row from left to right:
Alfonso XIII of Spain, George V of the UK and Frederick VIII of Denmark.
They were all related and a few years later their countries were at war with each other.
Thanks to @Piwowarczyk for posting this.