Later today, King Felipe of Spain and King Willem-Alexander of the Netherlands will be officially invested into the Most Noble Order of the Garter. Foreign Monarchs are made Stranger Knights and Ladies Companion of the Order of Garter, and are usually appointed to during a State Visit, but not officially invested until they attend an Order of Garter Service. King Felipe received the Order of the Garter in 2017, while King Willem-Alexander received it last year.
Queen Margrethe II of Denmark received the Order of the Garter during the Queen’s State Visit in 1979, being invested in 1980. King Carl XVI Gustaf of Sweden received it during the Queen’s State Visit to Sweden in 1983, being invested in 1985. King Juan Carlos of Spain got the Garter during the Queen’s State Visit in 1988, while Queen Beatrix of The Netherlands received it in 1989. Emperor Akihito of Japan was given the Garter in 1998, but it appears he was never formally invested. In 2001, the Queen gave the Garter to King Harald of Norway, and invested him the following year.
In 2002, Queen Margrethe of Denmark, Queen Beatrix of the Netherlands, Grand Duke Jean of Luxembourg, King Harald of Norway, and King Juan Carlos of Spain all attended the Order of the Garter Service while they were in the United Kingdom to attend a series of celebrations marking the Queen’s Golden Jubilee.
UPDATE- King Felipe and King Willem-Alexander were accompanied by Queen Letizia and Queen Maxima as they attended the 2019 Service of the Most Noble Order of the Garter at St George’s Chapel, Windsor.