Meghan Markle's mother due to meet Queen

Guy Faulconbridge and Michael Holden

Meghan Markle's American mother is due to take tea with the Queen, Prince Harry's grandmother, on the eve of a sumptuous royal wedding that will be watched by millions across the world.

Outside the ancient stone walls of Windsor Castle, home to the English royal family for nearly 1,000 years, well-wishers mingled with tourists and swarms of television crews under swathes of British and American flags.

Harry will marry Markle, a star of the TV drama Suits, in Windsor Castle's 15th-century St George's Chapel at a ceremony on Saturday.

Markle's African-American mother, Doria Ragland, was due to meet Queen Elizabeth, 92, for tea in Windsor on Friday. The yoga instructor charmed Harry's father, Prince Charles, when they met on Wednesday.

But it is still unclear who will walk Markle down the aisle after her father, Thomas, pulled out of the wedding in a family drama that was played out under the glare of global media attention.

Markle said she was sad he could not make it after he underwent heart surgery in Mexico.

For some black Britons, the prospect of a mixed-race royal princess has increased interest in the monarchy, which has so far been all white. A black American bishop is to give the address at the wedding.