<P> Assistant District Attorney Erin Reagan is Frank Reagan's sole daughter . She is portrayed by Bridget Moynahan . </P> <P> A New York County Assistant District Attorney and single mother, Erin is the second child and only daughter of the current New York City Police Commissioner Frank Reagan and his wife Mary . She grew up in Bay Ridge, Brooklyn, with three brothers, Danny, Joe, and Jamie . It is implied throughout the series that she had something of a wild streak growing up (unlike her daughter). In season 5, it is mentioned that she graduated top of her class from Columbia University; she later went on to attend Fordham University School of Law . In season 6, Erin celebrated her 40th birthday . </P> <P> Erin is divorced from John "Jack" Boyle (Peter Hermann), a criminal defense attorney, whom she met when they were 19 . In "Old Wounds", she finally changes her name from Erin Reagan - Boyle back to Erin Reagan . Since her divorce, Erin has had a few romantic interests . She and her boss, District Attorney Charles Rosselini (Bobby Cannavale), flirted with each other and even shared a kiss after a date, but nothing ever came of it mainly due to Erin's reluctance with the idea of dating her boss . In 2011, she met Jacob Krystal (Fred Weller) at an art gallery; she later learned that he was an art thief who returned once - stolen works to their rightful owners, and he left town . In 2013, after being shot in a courtroom hostage situation, she started up a fling with her ex-husband Jack but broke up when they started getting serious again (lest he break her heart again, or their daughter find out that they were once again "hooking up"). In 2014, she met Robert McCoy, a defense attorney, on a speed - date, and the two became romantically involved until he was appointed interim District Attorney, at which point she said she can't sleep with her boss . </P> <P> Erin is almost raped and killed in "Re-Do", though Frank saves her life by shooting her attacker dead . In "To Protect and Serve", Erin is taken hostage and shot in the arm at the courthouse . She is saved by Danny after he says a coded message, "Please, don't hurt my family," after which she dropped to the ground, and Danny shot her assailant . It is revealed that their father taught them this when they were young, as a plan in case one of them was ever held at gunpoint . </P>

Who plays the district attorney on blue bloods