Henry's father, Antoine de Bourbon, was the First Prince of the Blood, that is, the first male in line to the throne after Henry II and Catherine of Medicis's sons.
The marriage between Henry and Margot was a failure even before it had been done. First of all, a few months before the marriage, Jeanne d'Albret, Henry's mother, had been poisoned in France while negotiating peace with Catherine of Medicis and her son's marriage to Margot.
When they were married Margot was having a passionate affair with the Duke of Guise, with whom she would have loved to be married. During the wedding, when Margot had to say "yes" and accept Henry as her husband, she looked Guise for a while and said nothing. It was not until her brother King Charles IX ran to where she sat and hit her on her neck that she finally said "yes".
Then she refused to sleep with him and, a few days after the wedding, she took a new lover and the Saint Bartholomew Night massacre took place.
It was not a very good start, and it would become worst...