Luxembourg will enthrone a new head of state on Friday, as Grand Duke Henri abdicates his throne to son Guillaume. Grand Duke Henri, 70, will end his 25-year reign of the small European nation, that has a population of about 680,000 people, in a ceremony at the Grand Ducal Palace. The 43-year-old Guillaume will then be crowned and swear an oath to Luxembourg's constitution in front of guests such as the Dutch and Belgian royal couples.