Salman bin Hamad al-Khalifa, with Prince Charles in 2004. Campaigners want the Bahrain crown prince's royal wedding invitation revoked.
There will be at least one royal presence at Friday's wedding that is likely to raise eyebrows. Among the 46 foreign royals seated in the south lantern, just behind the British monarchy, will be Bahrain's crown prince, Salman bin Hamad al-Khalifa, an invitation that could prove awkward in light of his government's brutal treatment of mainly Shia pro-democracy protesters.
At least 30 people have died in Bahrain since protests began in mid-February, including four who died in official custody, and many activists and lawyers have been imprisoned.