DOVER, Del. (CBS) – Delaware’s Firefly Music Festival has finally announced its “mystery” headliner.

Beatle Paul McCartney is set to join the Kings of Leon and The Killers for the 2015 festival, which is scheduled for the end of June.

The announcement was something of a surprise, as McCartney had been a rumored headliner but was noticeably absent from the official lineup released a few weeks ago.

Firefly started back in 2012, and its attendance rapidly grew from 30,000 the first year to 80,000 in 2014.