Euphorbia X Pithyusa 'Rose's Surprise'

We do not know what it was, but the lovely dwarf Euphorbia pithyusa crossed with something in the garden, (possibly E. 'Golden Foam'), to produce this unusual plant, and we were surprised to see it producing seed. It forms a low dome of repeatedly branching red stems carrying countless yellow flowers. Will be happiest on a hot rockery or well-drained area. Let us know if you can solve this one.