13, Queen's Road Central.
It looks as though this building changed hands several times. In a 1909 advertisement it is described as 'Aster House (Late Connaught Hotel)'. Then Moddsey notes that later it changed it's name from Astor House to the St. Francis Hotel. Despite the change of name, it's function stayed the same - a hotel.
The 1909 advertisement uses the spelling 'Aster' throughout, even for the 'Telegraphic Address'. However in all other references I've seen, it is spelled 'Astor'.
As far as I can tell, it straddled the plots that today house Edinburgh Tower and York House. Later I'll overlay the different maps to get a clear answer for that.