Kate Middleton didn't wear her engagement ring that once belonged to Princess Diana at the Royal Marsden Hospital in London on Jan. 14. Inside why and more about Princess Kate's new ring.

For her first official solo appearance in over a year, Princess Kate met with cancer patients and the team at London's Royal Marsden Hospital.

Everyone just noticed that Kate Middleton isn't wearing her engagement ring...here's what we know about why she ditched the iconic sapphire.

Kate Middleton visited the Royal Marsden Hospital in London on Tuesday, Jan. 14, where she received chemotherapy treatment after her cancer diagnosis last year. See all the photos here

Kate, the Princess of Wales, made a poignant return Tuesday to the same hospital where she received treatment after being diagnosed last year with cancer.

Princess Kate Middleton opened up about the side effects of chemo when she visited the Royal Marsden Hospital in London, which is where she received treatment amid her own cancer battle. The Princess of Wales,

The Princess of Wales made a surprise return to the Royal Marsden Hospital to personally thank staff who looked after her during her cancer treatment on Tuesday. At such a critical moment in US history, we need reporters on the ground. Your donation allows us to keep sending journalists to speak to both sides of the story.

Middleton’s famous 12-carat diamond and sapphire engagement ring (you know, the one that used to belong to Prince William‘s late mother, Princess Diana) was MIA. And yes, this

Princess Catherine just made her first royal outing of the year—and this one hits pretty close to home. Earlier today, Kate Middleton paid a visit to The Royal Marsden, which happens to be the same cancer treatment center where she received her chemotherapy treatments following her cancer diagnosis.

Princess Kate made her first solo official appearance in more than a year as she visited the Royal Marsden Hospital in London to thank staff for her care

Kate Middleton just became an official patron of the hospital where she received preventative chemotherapy treatment, marking her first royal engagement of the year. During the outing, Kate visited with patients at the Royal Marsden Hospital,