On July 7 2005, four bombs exploded across London, killing 52 people and injuring hundreds more.
Bombs exploded on the tube, and on buses - devastating the capital - in a terror attack which shocked the world.
20 years on a memorial service will take place on Monday Jul 7 to mark two decades since the devastating incidents occurred and remember the lives lost.
To mark this significant anniversary, there will be a service of commemoration and other activities for those directly connected to the incident.
Already Prime Minister Sir Keir Starmer and London Mayor Sir Sadiq Khan laid wreaths at Hyde Park's 7/7 memorial on Monday morning, marking the time the first bomb exploded at 08:49 BST.
Sir Keir said the country would unite to remember the lives lost in the suicide attacks "and all those whose lives were changed forever".
King Charles also spoke out on the anniversary.
He said: “While the horrors will never be forgotten, we may take comfort from the way such events rally communities together in solidarity, solace and determination.
"It is this spirit of unity that has helped London, and our nation, to heal."
Here is all we know about the event:
Where is it taking place?
The event is a commemoration service, and is one of many taking place today remembering the victims of the bombings, which were carried out by Islamist extremists.
The commemoration event is a National Service of Commemoration taking place at St Paul's Cathedral.
The King will be represented by the Duke of Edinburgh, Prince Edward, and families of the victims will also be in attendance.
How to watch?
The event is an invitation only event, meaning people cannot just turn up.
But the London Assembly are sharing the event live online.
A live stream can be watched here from 11.15am. The event will start officially at 11.30am
The event can be watched here.
