Sting will join No Doubt for a special collaboration at the Global Citizen Festival, which returns to the Great Lawn in New York's Central Park on Sept. 27. Details on the "must see" performance remain under tight wraps, though celebrated live event and television producer Ken Ehrlich has offered some insight into how the team-up came to be. "In this case, it was pretty organic," explains Ehrlich, who joins the team to produce this year's show. "It came from No Doubt. We talked about a couple of possible people to do something with. As soon as we mentioned Sting, they loved that." Ehrlich, whose credits include 34 Grammy Award shows, is keeping tight-lipped on what track they'll perform. "It's a song that both acts are familiar with. I'm old, but I'm still a believer in the element of surprise, as much as we can. It's not easy in this age of tweets and the rest of it, but we're going to try," he tells Billboard. Sting's show The Last Ship is about to open on Broadway. Making the fest happen came down to an act of schedule juggling. "[Sting] was very excited about doing it. His desire to do it was quick, but it really came down to making sure scheduling worked," Ehrlich explains. Coinciding each year with the United Nations General Assembly meeting in New York, the Global Citizen Festival will once again be a free ticketed event, with the aim of helping to achieve a world without extreme poverty by 2030. Free tickets are now available at the Global Citizen web site, where users can take "action" by signing petitions and emailing world leaders (among other choices) to earn admission. Along with No Doubt and Sting, the likes of Jay Z, Carrie Underwood, fun., the Roots and Tiesto will perform at this year's event. Last year's Global Citizen Festival included performances from Stevie Wonder, Alicia Keys and John Mayer. The 2014 Global Citizen Festival will specifically focus on extreme poverty to children and young people across the world. Among the "actions" that music fans can complete to gain entry to the festival is the signing of a petition calling on world leaders to contribute to the GAVI alliance, which provides vaccines to children in impoverished countries. (c) Billboard