Prince William and Kate Middleton visited the French Embassy in London on Tuesday to offer their deepest sympathies to the victims of the Paris attacks.

Dressed in dark attire, the Duke and Duchess of Cambridge appeared somber as they signed a book of condolences with a message for the French people.

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"To all those who have died and were injured in the heartless attacks in Paris, and to all the people in France: nos plus sincères condoléances," the message read. It was signed "William" and "Catherine.”

On Friday, the President of France, Francois Hollande, declared a state of emergency after a series of shootings and explosions began at multiple sites throughout the French capital that left more than 100 people dead and nearly 400 wounded. Hollande has deemed the terror attacks -- which ISIS has since claimed responsibility for -- "an act of war."

Many other celebrities have spoken out about the attacks including U2, John Oliver and Madonna.

During a concert over the weekend, the “Material Girl” delivered a tearful message to the audience.

"I was gonna cancel my show tonight but then I thought to myself, 'Why should I give that to them? Why should I allow them to stop me and to stop us from enjoying freedom?” she told the audience. “All of the places where people were killed were places where people were having fun, people were enjoying themselves, eating in restaurants, dancing, singing, watching a soccer match.”

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“These are freedoms that we take for granted of course and we must not but they're freedoms that we deserve. We work hard, and we deserve to have fun, and there is no one in this world that should have the right to stop us from doing what we love!” she added.

“These are freedoms that we take for granted of course and we must not but they're freedoms that we deserve. We work hard, and we deserve to have fun, and there is no one in this world that should have the right to stop us from doing what we love!” she added.

U2 was supposed to perform two sold-out concerts last Saturday and Sunday but canceled in the wake of the tragedy. The band instead visiting the sites around the city where people were killed or injured and paid their respects.