Organisers of Latitude Festival have announced that Lily Allen will now headline after the frontman of Two Door Cinema Club collapsed in an airport while travelling to the UK.
The Northern Irish indie rockband said in a statement: "It is with a heavy heart that we are going to need to cancel our upcoming shows at Latitude and Bournemouth Academy.
"Alex collapsed at Seattle airport on the way to London and has been hospitalised with a chronic stomach complaint.
"We are devastated to have to cancel shows that we were so looking forward to. We can only apologise and hope for your understanding at this time. Love TDCC x."
The festival, which has been held in Henham Park in Suffolk since 2006, attracts more than 35,000 music fans and has seen headline acts such as Elbow and Paul Weller.
Event organisers announced that singer Allen will take the headline slot on the Obelisk Stage this Friday.
She said: "So sorry to hear about Alex from Two Door Cinema Club. However, I am more than happy to step in. I've never been to Latitude but I hear it's fabulous and I can't wait to get my heels on for some serious dancing action on Friday evening - so, so excited"
Organisers also hinted at another, as yet unannounced act taking a prominent slot on the Friday night.
Managing director of Festival Republic, Melvin Benn, said of the changes: "We wish Alex all the best and a speedy recovery. We are honoured that Lily Allen is able to step in at the last minute and would like to thank her for filling the headline slot.
"After her show-stopping performance at Glastonbury, Lily was a natural choice. The Latitude audience are in for something really spectacular."