The 76-year-old would have been the jewel in a crown of artists to have performed at the Mission Concert, including the Beautiful Noise of Carole King, Rod Stewart, Sting, Tom Jones, Eric Clapton, Engelbert Humperdinck, The Beach Boys, Kenny Rogers, Dionne Warwick and Ray Charles.
Obviously there will be thousands of disappointed fans in Hawke's Bay and beyond that were all set for a night of Yesterday's Songs.
The moment the breaking news went live comments poured in on to the Hawke's Bay Today Facebook page.
Endearingly, a large number of them were not posts airing their own grievances at missing out on seeing a living legend live. But rather sympathy for a man who will now start an incredibly challenging battle against a disease that is close to so many of us.
My best wishes go to Mr Diamond after receiving such awful news.
But, luckily for us, we'll always have the songs of the Solitary Man, If You Know What I Mean.