Supergirl 6x17 Season 6 Episode 17 Clip - I Believe in a Thing Called Love - Promo Trailer HD - Supergirl 6x17 "I Believe in a Thing Called Love" Season 6 Episode 17 Sneak Peek - LEX RETURNS - When Lex Luthor (guest star Jon Cryer) appears by Nyxly's (Peta Sergeant) side, Supergirl (Melissa Benoist) and team must deal with the emotional fallout of facing their two biggest foes at the same time. Alex (Chyler Leigh) makes plans for the perfect proposal to Kelly (Azie Tesfai), but work keeps getting in the way. The episode was directed by Jesse Warn and written by Dana Horgan & Nicki Holcomb (617). Original airdate 10/26/2021.