He struck a far more serious tone than we're used to.

Jimmy Fallon made a surprise appearance to give a commencement speech at the Marjory Stoneman Douglas high school graduation ceremony in Florida on Sunday, and the late night host praised the students for their activism and leadership after the mass shooting at their school in February.

"You are not just the future — you are the present. Keep changing the world. Keep making us proud," he told the crowd.

"You won't be classmates anymore. You'll be adults who will Facebook search each other at 2 in the morning for the next 10 years," he joked before continuing.

"First thing is this: When something feels hard, remember that it gets better. Choose to move forward. Don't let anything stop you. Every bad experience can have something good come out of it. You guys have already proved that. You took something horrific — instead of letting it stop you, you started a movement, not just here in Florida but around the whole world. The whole world has heard your voice and that was you making a choice. And that was you choosing hope over fear," he said to roaring applause.

What a great moment amid all the darkness.