Complex sentence: His family were the legitimate heirs to Monaco until 1911-18 (See Monaco Succession Crisis of 1918), and before 1911 Albrecht was intended to inherit Monaco, as his cousin Louis II, Prince of Monaco had no legitimate children.
Split into simpler sentences: His family were the legitimate heirs presumptive to Monaco's throne between 1911 and 1918 (See Monaco Succession Crisis of 1918). Before 1911 Albrecht was intended to inherit Monaco, as his cousin Prince Louis of Monaco had no legitimate children.