"Blue Bloods" has had many incredible guest stars over the years, and one of them is from the iconic film "Grease." Didi Conn, who played Frenchy in "Grease," made an appearance in Season 12, Episode 15 of "Blue Bloods" as Mrs. Devlin. In the episode, Frank handles the public's demands to defund the NYPD School Safety Division, while Danny and Baez assist a father in finding his missing ex and daughter. Conn expressed her surprise at the ongoing love for "Grease" and remembered her late co-star Olivia Newton-John fondly. The new episodes of "Blue Bloods" will premiere on October 7.