Margrethe II of Denmark has a son who is sixth in line to succeed the Danish throne, behind which elder brother?
Margrethe II of Denmark:  In 1967, she married Henri de Laborde de Monpezat, with whom she has two sons: Crown Prince Frederik (born 1968) and Prince Joachim (born 1969). Prince Joachim of Denmark:  Joachim is sixth in the line of succession to the Danish throne, following his elder brother, Crown Prince Frederik, and Frederik's four children.
Crown Prince Frederik