While attending a private screening of their hit show at New York City restaurant Lafayette on Thursday evening, Lewis was spotted also celebrating November's famous facial trend: a mustache.
"It's not for a role – I'm doing it for Movember," the actor, 42, told PEOPLE during the event.
The annual growing of mustaches for the month to increase awareness of men's health issues began over 10 years ago in Australia and has since become a worldwide phenomenon.
"A bunch of Aussies sat around drinking and thought it would be something fun to do – then they figured out the charity angle on it," Lewis tells PEOPLE, explaining that his own decision to skip out on shaving was inspired by his sibling.
"My brother actually runs a charity for prostate cancer research in England, and so I'm doing it in solidarity with him."
Reporting by CHARLOTTE TRIGGS