The most deadly terror attack in London in the past 12 years took place on Wednesday, when a man stabbed a police officer and drove an S.U.V. into pedestrians outside Parliament. At least four people were killed, an additional 40 were injured, and Parliament was evacuated. Prime Minister Theresa May condemned “the sick and depraved terrorist attack on the streets of our Capital this afternoon.”

The Queen—who was in Buckingham Palace yesterday when the attack occurred—issued a statement Thursday morning in which she explained why she and Prince Philip would not be appearing as scheduled at New Scotland Yard today.

“Following the shocking events in Westminster, Prince Philip and I are sorry that we will not be able to open the New Scotland Yard building as planned today, for very understandable reasons. I look forward to visiting at a later date.

My thoughts, prayers, and deepest sympathy are with all those who have been affected by yesterday’s awful violence.

I know I speak for everyone in expressing my enduring thanks and admiration for the members of the Metropolitan Police Service and all who work so selflessly to help and protect others.”

The Duchess of Cambridge did make an appearance in London as scheduled on Thursday for a screening of short films. Per Daily Express reporter Richard Palmer, Kate, in her remarks, “recalled yesterday's Westminster attacks and spoke out in memory of the victims.” “I know you will all want to join me in sending our thoughts and prayers to all those sadly affected by yesterday's terrible events in Westminster,” she said as part of her speech.