Academy Award-winning actor Leonardo DiCaprio praised teen activist Greta Thunberg in an Instagram post on Friday, calling her "a leader of our time."

He said, "It is because of Greta, and young activists everywhere that I am optimistic about what the future holds." He also said he spent time with her, calling it an "honor."

"She and I have made a commitment to support one another, in hopes of securing a brighter future for our planet," DiCaprio said in his post, alongside two pictures of him and Thunberg.

DiCaprio has been a vocal environmental activist for years through the Leonardo DiCaprio Foundation, which partners with projects that protect vulnerable wildlife from extinction. He's produced several documentaries on climate change and animal rights, including "The 11th hour," "Sea of Shadows," "Cowspiracy," "Catching the Sun," "Before the Flood," "The Ivory Game," "A Plastic Ocean" and "Virunga."

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Thunberg has become known worldwide for her weekly climate strikes, which she started on her own in 2018. Since then, the teenager has inspired millions of people to spend their Fridays urging their governments to take action against climate change.

Her movement has resulted in the largest climate protests in history.

"I hope that Greta's message is a wake-up call to world leaders everywhere that the time for inaction is over," DiCaprio said.

Thunberg spoke on Friday at a climate rally in Los Angeles and mentioned wildfires that have recently devastated parts of California. "Everywhere around the world, we can see these horrible environmental feedbacks that countless people are suffering and dying from," she said.

"The scientists have been repeating the same message over and over again, and yet, they are still not being listened to," Thunberg continued. "Why are the people in power still pretending that everything is fine and we can just continue to live … as if there was no tomorrow? Well, there is a tomorrow — it is a tomorrow where we, the young people, will live and we need to fight for that tomorrow as if our lives depend on it, because it does."