The Almanach de Gotha was the most important genealogical reference book for Europe's Royal and Aristocratic houses, and it was, until the Second World War, regarded as the definitive resource.  From 1925, the year after he succeeded to the headship of the Russian Imperial House, Grand Duke Kirill was listed as the Dynastic Head, and his son Grand Duke Wladimir listed as his heir.  The two morganatic children of Prince Roman Petrovich, Nicholas and Dimitri R. Romanov were not even listed, as they were non-dynastic issue, and therefore not members of the Imperial House. (Cf. page 107, where they are listed as "de ce marriage sont issus deux fils." [from this marrige issue two sons} The marriage itself, to Countess Praskovia Sheremetev, is described as "pas conforme aux lois de la maison." [not in conformity to the laws of the House.])