Charles “is pleased to be able to welcome Ms. Markle to the Royal Family in this way,” the palace said.

The news comes as the final wedding preparations swing into gear. Union Jacks have been unfurled, security barriers are up and fans are already moving in to capture the prime viewing positions. The world’s media have descended on this town of 32,000 known for a castle whose site was chosen by William the Conquerer. Windsor is about 25 miles (40 kilometers) west of London.

Markle’s mother, Doria Ragland, was the bookies’ favorite to escort the bride, but Prince Charles has a lifetime of experience in appearing at large-scale public events amid intense scrutiny.

Having the father of the groom escort the bride is yet another twist in a royal wedding that is proving to be different from many others. Normally such occasions are choreographed to the second — and replete with tradition.