Earrings that belonged to the mother of Diana, princess of Wales, and were supposed to be part of a U.S. exhibition of Diana's belongings have been shipped back to one of Diana's sisters — who will wear the jewels at the nuptials of Prince William and Kate Middleton.

KANSAS CITY, Mo. — You could call it the Case of the Missing Diamond Earrings.

Except in this mystery, we know where the earrings disappeared to.

A pair worn by Diana, Princess of Wales, at her wedding nearly 30 years ago arrived in late February at Kansas City, Mo.’s, Union Station along with everything else in the “Diana: A Celebration” exhibit.

But the 40,600 visitors who have seen the show so far haven’t seen the earrings.

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They were sent back to England before the show opened March 4.

Watch your TV closely on Friday, the day Prince William and Kate Middleton wed. You might catch a glimpse of the earrings sparkling on the ears of Lady Sarah McCorquodale, Diana’s oldest sister.

She and Diana’s two other siblings — Lady Jane Fellowes and Charles Spencer — will be seated across the aisle from the royal family, behind Kate Middleton’s parents, in Westminster Abbey.

The earrings once belonged to the siblings’ mother, Frances Shand Kydd, who died in 2004. Each earring has a pear-shaped diamond surrounded by nearly 50 smaller diamonds.

Diana’s mother lent them to her for her first public appearance after she and Charles announced their engagement.

On her wedding day in 1981, they were the “something borrowed” in Diana’s wedding attire.

“They physically were here in Kansas City, but they never got unpacked and put on display,” said Tony Cook, a Union Station spokesman.

Cook doesn’t expect the earrings to return to the exhibit, which wraps up June 12.