Robert C. Johnson 2/2019:

'YellowBird' Johnson/Adelman (Salmon Dream x Lemon Chiffon) First offered in 2019 in limited numbers, from my first batch of seedlings bloomed in 2008. Divisions from this first offering went to Sweden and Russia, as well as to growers in the US. Flowers up to 10" in diameter under ideal conditions. Roots are notably resistant to root diseases, and in many circumstances flowers are more resistant to stamen-browning from spring rains than 'Lemon Chiffon'.

Carsten, You are welcome to use the picture of my sister.  It's always been one of my favorites, and gives a pretty good idea of just how large these blooms can be.  At the Adelmans, that is.   You probably remember just how well things grow there.