"The most obvious triangle that you see in the pilot -- literally that you see -- is Francis and his half-brother, Bash [and Mary]," McCarthy points out. "But really, underneath that is a bigger triangle, which is Mary, Francis and France. Or Mary, Francis and duty."
‘Reign’ interview: Love triangles and the history of Mary, Queen of Scots - Zap2it
There is a big difference between what the writers intend to write and what the channel decides to promote. We've all had our fair share of misleading promos in the past, in every single fandom I've been, the difference between what is promoted and what actually happens on your screen is always big.