Zayn Malik has pulled out of a performance at the Capital FM Summertime Ball because of an "anxiety" attack.
The former One Direction star, who was due to perform at the Wembley Stadium show, posted a lengthy apology and explanation on his Instagram account.
"Unfortunately, my anxiety that has haunted me throughout the last few months around live performances has gotten the better of me," he said.
"With the magnitude of the event, I have suffered the worst anxiety of my career. I cannot apologise enough.
"I promise I will do my best to make this up to everybody I've let down today."
The show's organisers were forced to make an announcement just moments before Malik was due on stage on Saturday.
The news was greeted with loud boos from disappointed fans.
Capital FM said in a statement: "We know everyone's already had a great day and enjoyed the 19 other huge artists' performances, but of course we're all gutted that Zayn's had to pull out tonight at the last minute."
Following Malik's message, many people have voiced their support for the 23-year-old Bradford-born star.
This Morning's Phillip Schofield tweeted: "I have huge respect for Zayn with this."
Malik's decision to pull out of the Summertime Ball follows a number of non-appearances by the singer.
In January, he pulled out of The Graham Norton Show due to "scheduling" issues.
A month later, he cancelled a Radio 1 interview with DJ Greg James, a move which was criticised at the time as "rude" by Piers Morgan.
The Capital FM Summertime Ball, which raises money for charity, would have been Malik's first live UK solo stage performance.