Los Angeles: Hollywood star Leonardo DiCaprio, who was set to host a fundraiser for US presidential hopeful Hillary Clinton, had to bow out due to a scheduling conflict. His friend Justin Timberlake stepped in. "Leonardo DiCaprio was scheduled to host a fundraiser with Hillary Clinton on Tuesday (August 23) at his home in Los Angeles," a source close to the event told people.com. "Unfortunately, Leonardo is stuck in New York until Wednesday (August 24) to finish his current project." The Oscar winning actor then called up Timberlake and Jessica Biel to take his place. "Not wanting to leave Hillary hanging, Leonardo called his friends Justin and Jessica Biel and asked if they would host for him. They immediately agreed to fill in as hosts and moved the event to their home for Tuesday," the source added. DiCaprio, 41, is producing the documentary "Before the Flood" and that's what's keeping him busy. The film, expected to premiere at the Toronto International Film Festival on September 9, focuses on the effects climate change have on endangered species, ecosystems and native communities. It will feature US President Barack Obama, Bill Clinton, Secretary of State John Kerry, United Nations Secretary-General Ban Ki-moon and Pope Francis. DiCaprio is a fervent supporter of the Clinton campaign. In June, he attended another star-studded fundraiser at entertainment exec Harvey Weinstein's New York home.