Interesting! On the RHS there is Hydrangea macrophylla Great Star = 'Blanc Bleu', which is not a paniculata and looks nothing like it..
http://apps.rhs.org.uk/horticu...
But it has the same "princesse Sturdza" origins..
http://www.promessedefleurs.co...
http://www.esveld.nl/htmldia/h...
I didn't get any results for The Swan..
http://apps.rhs.org.uk/rhsplan...
I'm as confused as anyone! The RHS search only lists plants which are sold by nurseries here and are listed on their site, but if Heronswood is selling it as The Swan maybe that's the correct name?
Zuzu, I'm getting as old as treasure.