I don't think he's racist, i think he's a twat. He drew comparisons to the IRA/Troubles straight after the Boston Bombings and had a mini backlash about it so I think he should be hyper aware of how tweets could be interpreted even if there is no malice behind it.
The firing might be over the top but what can you expect for an employee of a national broadcaster making a potentially racist joke about a member of the Royal Family.
The firing might be over the top but what can you expect for an employee of a national broadcaster making a potentially racist joke about a member of the Royal Family.