I watched the Mayor of London Sadiq Khan's response to this Wednesday's horrific terrorist attack at Westminster and not only did it remind me so much of the horrific 7/7 attacks in London twelve years ago when I was Mayor, but also the amazing response of ordinary Londoners of all colours and creeds.
The spirit of unity we have seen since the attack has shown again that we are a great city and that we are not going to be divided by the terrorists.
When I was Mayor, after the 2001 attacks in the US, we put vast amounts of public money into building up police resources to deal with the possibility of terrorist attacks, and every year three or four potentially major incidents are foiled by our police and security services.
Today, just as in the years leading up to the 2005 bombings, our police, fire brigade, transport staff and NHS are amongst those who put a massive effort into examining the risks of a terrorist attack and how to respond.
The thousands who took part in preparation for how we would respond to those horrific attacks in 2005 will never be famous -- but they know the work they did reduced the loss of life and prepared the capital for a remarkably swift return to normal.
In the hours and days that followed the attacks in 2005, I heard so many amazing accounts.
The Tube cleaners who were leaving work but turned around and went back with bottles of water to comfort the victims. I met the surgeons who worked relentlessly to try and save lives and the Tube and bus workers who made sure the system was up and running the following morning.
Again this week I was proud of this city and its public servants.
Tragically, one of these public servants, PC Keith Palmer, a Metropolitan Police officer was among those killed this week as he did his duty in protecting us. He was 48 and a husband and father.
When deciding on our response to the bombings in 2005, central to our thoughts was that a key objective of the terrorists was to cause an anti-Muslim backlash and that was always a risk.
Yet perhaps the most wonderful thing about London's response was that we were not aware of any single incident of violence or abuse being directed against the city's Muslims. Londoners' response was watched around the world and in the weeks that followed, tourism numbers went up and people still continued to come to London to make it their home.
That day of tragedy and its afternath showed London at its finest. Londoners recognised what these terrorists wanted to do was to tear us apart, in order to unleash a wave of hatred, antagonism and violence. We didn't allow the terrorists to divide us.
And that's how we have to respond today - the Muslims that live in London, who have become Londoners, are not responsible for what has happened here.
The fact that last May, with all the attempts to whip up Islamophobia, the people of London voted for a Muslim Mayor shows that we are a great city that finds strength in its diversity. We are one London. We are not going to be divided by the terrorists. We've got to make certain that terrorist attacks - whether it is an international terrorist organisation or an angry young man - cannot divide us. We have to be united.
As Sadiq Khan said this week," Londoners will never be cowed by terrorism. We stand together in the face of those who seek to harm us and destroy our way of life. We always have, and we always will."
Until the day I die, I will always be proud to have been mayor of this wonderful city and its people