Kate Middleton wasn’t wearing her famous engagement ring (which once belonged to Princess Diana) during a royal visit at Great Ormond Street Hospital earlier today. Instead, she wore a simple gold band in its place. But her decision to forgo the ring was driven by practical reasons—she was following the hospital’s policy on minimal jewelery, People reports.
The Duchess of Cambridge visited the hospital to open the new Mittal Children’s Medical Centre, which provides care for young patients. As she toured the new facility, she met with some of children being treated and joined in on arts and crafts activities. According to People, the duchess had to wash her hands before entering the treatment areas, so removing jewellery was recommended.
Middleton put the ring back on after the morning visit, however. She was seen wearing it once again at her next event with the Wimbledon Junior Tennis Initiative.
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The Duchess of Cambridge’s ring is a precious piece of jewellery, which consists of a 12-carat center sapphire surrounded by 14 diamonds. It’s estimated to be worth $500,000, E! reports, even though it was originally only worth about $47,000 when Prince Charles proposed to Princess Diana with it in 1981. The ring apparently even costs more than Queen Elizabeth‘s, which is said to be valued at $168,480.
Prince William proposed with the the sparkler in Kenya in October 2010. He and Middleton tied the knot five months later, in April 2011. Since then, the Duchess of Cambridge has rarely taken it off. She was even seen wearing it during her royal engagements within the past week.
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This article originally appeared on Harper’s BAZAAR US.