James MacMillan, The Sacrifice (2005-06), opera in three acts, libretto by Michael Symmons Roberts after the Branwen story in the Mabinogion; world premiere 22 September 2007 at the Donald Gordon Theatre, Wales Millennium Centre, Cardiff, staged by Welsh National Opera. Sources: https://en.wikipedia.org/wiki/The_Sacrifice_(opera) , and the inlay of Chandos CHAN 10572(2) scanned in the rip being filed, which heads it "the sacrifice (2005-06) / Opera in Three Acts / Libretto by Michael Symmons Roberts / Based on a story from The Mabinogion". A staged opera, so within scope; findopera already holds MacMillan Clemency (opera 2488).