King Charles III led commemorations on Monday on the 20th anniversary of the 2005 London transit bombings — the deadliest attack on the British capital since World War II.

Fifty-two people died and more than 700 were wounded when four British men inspired by Al-Qaida blew themselves up on three subway trains and a bus during the morning rush hour on July 7, 2005. They were the first suicide bombings on European soil.

The anniversary will be marked with a ceremony at the 7/7 memorial in Hyde Park and a service of commemoration at St Paul’s Cathedral. In a message, Charles said his “heartfelt thoughts and special prayers remain with all those whose lives were forever changed on that terrible day.”