Zayn Malik has pulled out of a performance at the Capital FM Summertime Ball citing "anxiety" for his absence.
The former One Direction star posted an apology and full explanation in a message on his official Instagram account on Saturday.
He said: "To all those people who have been waiting to see me perform at the Capital Summertime Ball today ... I flew into the UK last night to appear in my home country in front of my family, friends, and most importantly my UK fans.
"Unfortunately my anxiety that has haunted me throughout the last few months around live performances has gotten the better of me ... with the magnitude of the event, I have suffered the worst anxiety of my career."
He added: "I cannot apologise enough, but I want to be honest with everyone who has patiently waited to see me, I promise I will do my best to make this up to everybody I've let down today.
"I know those who suffer anxiety will understand and I hope those who don't can empathise with my situation."
In a statement, Capital FM confirmed Zayn would not be appearing at the event in Wembley.
"We're very sorry we've just been told that due to illness Zayn will not be performing at today's show.
"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."
The statement ended with Capital FM "wishing him better."
The station also posted a tweet to their official account.
On Twitter, This Morning's Phillip Schofield tweeted his support, saying he had "huge respect" for Zayn.
The decision to pull out of the Summertime Ball follows a number of non-appearances from the Pillowtalk singer.
In January, the Bradford-born star 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 TV star Piers Morgan.
The Summertime Ball, which raises money for charity, saw the likes of Little Mix, Ariana Grande and Years & Years take to the stage.