A portrait of Dafydd Iwan called ‘Rouser at the Red Wall’ has been ‘lost’ in transit on its way to an auction to benefit the ‘Yes Cymru’ campaign.
Mr Iwan is currently enjoying number one in the iTunes charts, after his patriotic anthem 'Yma O Hyd' climbed to the top spot following Wales' historic World Cup qualification.
The courier service UPS is said to be investigating the loss.
The artist of the portrait, Dan Llywelyn Hall, is known for other depictions including that of the Queen, Amy Winehouse and WW1 veterans.
The painting, which was unveiled by Dafydd Iwan in Machynlleth earlier this year, was to be a highlight in the prestigious ‘Welsh Sale’ in Cardiff.
Mr Llywelyn Hall has expressed ‘mortification’ at the apparent vanishing of the painting measuring 4x3ft.
He is offering a choice of painting as a reward for the return.
Dafydd Iwan's song 'Yma O Hyd' was originally released in 1981, with it telling the story of how Welsh language and culture has survived more than 2,000 years against all the odds.
"The 1980s weren't good times for Wales," Dafydd said.
"The mines were closing, the factories were closing, we'd just lost the referendum - it looked miserable and we felt it needed a boost.
"So Yma O Hyd was written as a booster and to say: 'Ok, we've had tough times, and we've been through it all - we've been here 1600 years and counting."
The song has now become an unofficial anthem for the Wales national team after qualifying for their first World Cup since 1958.