Chart star Jessie J has pulled out of a headlining show tonight on medical advice after being diagnosed with a "fatigue" virus.
The singer apologised to fans for cancelling her show in Pontypridd, Ponty's Big Weekend, which has prompted the first night of the three-day event to be axed.
Show bosses said the singer is suffering from cytomegalovirus (CMV) which they said had caused her "considerable fatigue".
In a message on her website Jessie said: "I have been diagnosed with a viral infection recently that has caused me to be extremely fatigued.
"I was hoping to be better but I have been to see my doctor this morning after not feeling great who has advised me I am still in need of rest and to perform will make me worse."
Jessie, a judge on BBC1 talent series The Voice, said she wanted to "personally apologise" to fans and was "just not well enough" to appear.
"Back to bed I go - so sorry," she added.
The Price Tag star had to cancel a number of shows last summer after damaging her ankle during a fall.
CMV is said to be a common virus with no cure and is part of the herpes family.
Fans have been told they will get their money back.
Further shows starring Olly Murs and Alfie Boe over the weekend are unaffected.
Christian Hanagan, of Rhondda Cynon Taf Council, said: "We wish Jessie well in her treatment and hope she is back on her feet soon."