Green Day was scheduled to perform at Bologna's I-Festival on Sunday night when the 40-year-old "Time of Your Life" singer was unexpectedly rushed to the hospital. The band has not released details nor specified Armstrong's illness, but bandmates Mike Dirnt and Tre Cool did release a short video for fans on the band's website, in an effort to explain what had happened and apologize for the sudden cancellation.
"Obviously, you know, we apologize profusely," began Dirnt, "this is really unfortunate, but ... Billie got rushed to the hospital last night due to illness, and you know, the doctors don't think it's a good idea for him to play today."
Armstrong, who is scheduled to head to Las Vegas with Green Day for their next performance on Sept. 21 at Ryan Seacrest's iHeartRadio festival, looked recovered when he returned to Los Angeles on Tuesday but pointed to his throat and mouthed to reporters that he had lost his voice, reported TMZ.
Although the band has stayed mum on the specifics of Armstrong's hospital visit, Green Day fans tweeted that Armstrong was the victim of severe stomach cramps.
"We're beyond devastated. We're as sad as you guys are," added Cool. "Billie's extremely upset about it, and we'll see you very soon."
"We love you guys and we'll be back as soon as we can," said Dirnt.
After rumors began to swirl that Armstrong had died, the singer and guitarist posted a picture of himself to Instagram, along with a message for his fans. "I'm alive," declared Armstrong. "Bologna we will be back! I promise with all my heart!! Rage and love Billie joe."
His wife, Adrienne Armstrong, also took to social media to express her appreciation for show of concern and support, tweeting on Monday, "Thanks for all the love & well wishes. He is feeling better .. ??"
Armstrong's health concerns don't appear to have slowed down his band, however. Green Day is preparing to release three albums over the course of the next four months. "¡Uno!", "¡Dos!" and "¡Tre!" will be individually released on Sept. 25, Nov. 13, and Jan. 15.