I think he goes under the name Lancelot because Mc said nobody knew he's ”night activities”, and nobody really saw Lancelot? The only information about Lancelot came from maids who probably doesn't recognize Ares himself and in novel Lancelot didn't even described, he was just randomly helping area and then just disappeared. So I'm betting in that Lancelot is his alias.
lmaooo she should have questioned a bit more about this 'lancelot' since his background story is too good to be true hahaha
but he told the fl that Lancelot was his friend after they slept together? I don't think there'd be reason for him to lie after he already told her his real name
Then who r they calling lancelot that night!? I clearly read it they called him that !? Right!? Right!!?? Σ(っ°Д °;)っ