<P> He has made appearances in several commercials, such as the anti-tobacco "Fair Enough" ads . In 2006, he starred as Jeremy Glick in the feature film, United 93 . </P> <P> Hermann was in the Broadway premiere of Eric Bogosian's Talk Radio, starring Liev Schreiber, and featuring fellow Law & Order: Special Victims Unit cast member Stephanie March . It began performances on February 15, 2007, in preparation for a March 11 opening; its final Broadway performance was on June 24, 2007 . </P> <P> He also guested on 30 Rock during its first season, and starred in ABC's mid-season replacement series, Cashmere Mafia, as Davis Draper . As of 2011 he appears in the Broadway play War Horse, and makes occasional appearances as Erin Reagan's ex-husband John "Jack" Boyle on Blue Bloods . </P> <P> As of August 2017, he is on Younger which is in its fourth season . In March 2018, HarperCollins published Hermann's children's book If the S in Moose Comes Loose . </P>

Who plays erin reagan's husband on blue bloods
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