Grand Duke of Luxembourg’s Address

I have been asked whether there is a campaign to support Grand Duke Henri of Luxembourg for his refusal to be complicit in the legalization of euthanasia in his country, and if so, what the address is to support him. I believe there is such a campaign. But the only address I have at the moment is slow mail:

H.R.H. Grand Duke Henri of Luxembourg

Palais Grand-Ducal L-1728 Luxembourg,

Luxembourg