Rachel Getting Married

Kym (Anne Hathaway) is released from rehab for a few days so she can go home to attend the wedding of her sister Rachel (Rosemarie DeWitt) in her Connecticut home town. She is picked up from the clinic by her father and his new wife. Upon arrival at Rachel's house where the wedding is to be held, the atmosphere is strained between Kym and her family members as they struggle to reconcile themselves with her past and present. Kym's father shows intense concern for her well-being and whereabouts, which Kym interprets as mistrust. She also resents her sister's choice of her best friend Emma (Anisa George), rather than Kym, to be her maid of honor. Rachel, for her part, resents the attention her sister's drug addiction is drawing away from her wedding, a resentment that comes to a head at the rehearsal dinner, where Kym, amid toasts from friends and family, takes the microphone to offer an apology for her past actions, as part of her twelve-step program.Underlying the family's dynamic is a tragedy that occurred many years previously, which Kym retells at a Narcotics Anonymous meeting. As a teenager, Kym was responsible for the death of her young brother Ethan, who was left in her care one day; driving home from a nearby park, an intoxicated Kym had lost control of the car, driving over a bridge and into a lake, where her brother drowned. Kym and the whole family apparently never recovered from the shock.The day before the wedding, as Rachel, Kym, and the other bridesmaids are getting their hair done, Kym is approached by a man who she knew in an earlier stint in rehab. He thanks her for the strength she gave him through a story that Kym told out loud in rehab about having been molested by an uncle and having cared for her sister, who was anorexic. Rachel, hearing this, storms out of the salon. The story, it turns out, was all a lie an apparent attempt by Kym to evade responsibility for her addiction.The sisters' fight comes to a head later that night at their father's house, when Kym comes home. As it turns out, Rachel still blames her for Ethan's death. This causes her to leave, after eventually admitting to being high while she was a teen and heads to their mother's house, hoping to find solace with her. However, a fight breaks out there, too. Kym confronts her mother, Abby, about it and demands to know why she left Ethan in her care while she was under the influence and not Rachel's. She soon realizes that her mother is denying any responsibility that Kym has for his death, by trying to tell her that she was good to him and that her sister is wrong in her accusation. Kym tells her mother that she was also responsible for the boy's death, and Abby slaps her in the face. Kym hits her mother back and runs off again in her father's car. While driving away, she is seen crying because, while she started to accept responsibility for what she has done, her mother has failed to do the same. This time, she intentionally crashes her father's car into a giant rock, and spends the night in the wreck.The next morning, the day of the wedding, Kym is awoken by police. After passing a sobriety test, she gets a ride home. She makes her way to Rachel's room, as Rachel prepares for the wedding. Seeing Kym's bruised face from a fight she had with their mother, the anger of the previous night vanishes, and Rachel tenderly bathes and dresses her sister.Amid a festive Indian theme, Rachel and her fiancé are wed. Kym is the maid of honor, and is overcome with emotion as the couple exchange their vows. Kym tries to enjoy herself throughout the wedding reception but continues to feel out of place and is nagged by the unresolved dispute with her mother. Ultimately, her mother leaves the party early, despite Rachel's effort to bring the two together, and the riff between Kym and her mother is left unreconciled.The next morning, Kym must return to rehab. As she is leaving to go to the bus station to catch her bus back to the city, Rachel runs out of the house to hug and kiss her goodbye. Kym agrees to stay in touch.

Question: How did kym's brother die?