Ethos didn't know about the curse that befell his cousin, the crown prince. Only select family members were informed about this. Athos was one of them because Mars really trusted him.
Mars told Athos this big secret five years ago and Athos kept this from anyone else, even his own brothers. So, during this mission, Mars didn't tell Ethos the truth about the reason why he came to Wintermere.
Mars only told his younger cousin that he was doing a regular inspection throughout their empire and its colonies since he would soon take the throne.
He wanted to know the situation in the colonies and asked for feedback from the respective governors on how they could do things better at the central level.
The crown prince was so good with words that he could easily evade any suspicion on his true intention of traveling to Wintermere.
