Currently, 15-year-old Xiuhtezcatl Martinez is leading a legal challenge that may get the United States government to change its stance on fossil fuel projects. Already a noted environmentalist, he and a group of teenagers are suing the government for their inaction on climate change. On Earth Day, Xiuhtezcatl headed to the United Nations in New York City, where 171 world leaders gathered to sign a global climate pact called the Paris Agreement, according to CBS

The pact is an agreement for countries to take action on climate change, so for Xihtezcatl, who spoke at the event, it marked an important step forward. His Facebook page is filled with images and news of his time at the UN. “Yo Family, I have been in the UN the last two days and it has been awesome,” he wrote. “Victoria my friend and comrade in the climate movement and lawsuits owned the UN, working interviews in the media zone and dropping speeches from the younger generations that lit the room on fire. Things are changing! The signing of the Paris agreements are today and the entire planet knows they are not strong enough. The people are ready to fight for everything the leaders were afraid to put in the agreement. Even the UN knows we need to do better and fight for more ambitious goals that will actually defend out future and protect our Earth.”

Among the many people who attended the event, Leonardo DiCaprio is one of the most recognizable names. DiCaprio has long been an environmental ally. Before winning his Oscar this year, he donated $15 million for environmental projects – with $3.4 million going to the indigenous groups of the Ecuadorian Amazon, and he also denounced oil companies for their role in the Peruvian oil spill.

On Friday, Xiuhtezcatl and Leo met, and the young activist couldn’t contain his excitement. “Just spent time with Leonardo DiCaprio at the United Nations!” he captioned the photo of the two of them. “He inspired my work at 6 years old with his movie The 11th Hour. So awesome to finally connect with him!”

Leonardo DiCaprio also spoke at the UN chat, check it out below. And then check out what others had to say here.