Prince William and Kate Attend the Festival of Remembrance Donning Red Poppy Pins

This Sunday, November 14, marks Remembrance Sunday in the UK, a holiday celebrated after Remembrance Day on November 11 to commemorate the British soldiers who fought in conflicts throughout England’s history. The royal family has been making appearances all week to show their respects to servicemen and women, and on Saturday Prince William and Kate Middleton attended the Festival of Remembrance at Royal Albert Hall in London.

While plenty of other royals were in attendance—including Prince Charles and Camilla, Prince Edward and Sophie, Countess of Wessex, and others—the Queen was notably absent after her recent hospitalization, which has seen her taking a break from royal duties. Though she initially intended to go to the Remembrance Sunday wreath-laying the following day, at the Cenotaph memorial, she had to pull out at the last minute over a back sprain, according to the BBC.

As is tradition, Kate and the other women in attendance wore black, while the men wore suits. Each attendee also donned a red poppy pin, a symbol of Remembrance Day that was started by the veteran’s charity Royal British Legion 100 years ago this year, according to People.

The poppy pin, which is typically worn from All Souls Day on November 2 to Remembrance Sunday, is thought to be a nod to a World War I poem from 1915 called Fields of Flanders by John McCrae, a Canadian officer. The first lines, which describe how flowers grew over the graves of soldiers, read:

In Flanders fields the poppies blow
Between the crosses, row on row,
That mark our place; and in the sky
The larks, still bravely singing, fly
Scarce heard amid the guns below.

Some Remembrance Day participants can also be seen wearing black poppies, to commemorate the contributions of Black, African, and Caribbean servicemen and women to British war efforts. It's a solemn and important day in the British calendar, so it's no wonder the royals have spent the week paying their respects.