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.
Human rights campaigners are already petitioning the foreign secretary, William Hague, to revoke the invitation, saying the prince should not be allowed to attend given the bloodshed in his country. Earlier this week, the crown prince praised the "relentless efforts of Bahrain's security forces to maintain security and stability".