The Royal Tenenbaums

Royal Tenenbaum explains to his three children, Chas, Margot, and Richie, that he and his wife, Etheline, are separating. Each of the Tenenbaum children achieved great success at a very young age. Chas is a math and business genius, from whom Royal steals money. Margot, who was adopted by the Tenenbaums, was awarded a grant for a play that she wrote in the ninth grade. Richie is a tennis prodigy and artist. He expresses his love for adopted sister Margot through many paintings. Royal takes him on regular outings, to which neither of the other children are invited. Eli Cash is the Tenenbaums' neighbor, and Richie's best friend.
Twenty-two years later, Royal is kicked out of the hotel where he has been living. All of the Tenenbaum children are in a post-success slump. Richie is traveling the world in a cruise ship following a breakdown. He writes a letter to Eli revealing his love for Margot. Chas has become extremely overprotective of his sons, Ari and Uzi, following his wife Rachael's death in a plane crash. Margot is married to neurologist Raleigh St. Clair, from whom she hides her smoking and her checkered past. Raleigh is conducting research on a subject named Dudley Heinsbergen. Etheline's longtime accountant, Henry Sherman, proposes to her.
Learning of Henry's proposal, Royal claims that he has stomach cancer in order to win back the affections of Etheline and his children. He moves into the family home and sets up medical equipment in Richie's room. Etheline calls each of her children home. Royal learns of Chas' overprotective nature and takes his grandsons on an adventure involving shoplifting and dog fighting. Upon their return, Chas berates him for endangering his boys. Royal accuses Chas of having a nervous breakdown.
Eli, with whom Margot has been having an affair, tells her that Richie loves her. Royal discovers the affair and objects to Margot's treatment of Raleigh, who confides to Richie his suspicions of Margot. He and Richie hire a private investigator to spy on her.
Henry investigates Royal's cancer claim and discovers the hospital had closed years before, his doctor does not exist, and that his cancer medication is only candy. He confronts Pagoda, the family servant, and gathers the whole family to tell them what he's discovered. Afterward Royal and Pagoda move out of the house.
Richie and Raleigh get the private eye's report on Margot, which reveals her history of smoking and sexual promiscuity, including a previous marriage to a Jamaican recording artist. Raleigh is only concerned by her smoking, but Richie takes the news much harder. He goes into the bathroom, shaves off his hair and beard, and calmly slashes his wrists. Dudley finds him in a pool of blood, and Raleigh rushes him to the hospital. As the Tenenbaums sit in the waiting room, Raleigh confronts Margot and then leaves. Richie escapes the hospital and meets with Margot. They share their secret love and they kiss.
Royal decides that he wants Etheline to be happy. He arranges for a divorce. Before Henry and Etheline's wedding, Eli, high on mescaline, crashes his car into the side of the house. Royal rescues Ari and Uzi, but the boys' dog, Buckley, is killed. Enraged, Chas chases Eli through the house and wrestles him to the ground. Eli and Chas agree that they both need psychiatric help. Chas thanks Royal for saving his sons and for buying them a Dalmatian from the responding firemen as a replacement for Buckley. Forty-eight hours later, Etheline and Henry are married in a judge's chambers.
Some time later, Margot releases a new play inspired by her family, Raleigh publishes a book about Dudley's condition, Eli checks himself into a drug rehabilitation facility in North Dakota, and Richie begins teaching a junior tennis program. Chas becomes less overbearing and overprotective of his children. Royal seems to have improved his relationship with all of his children, and seems to be on better terms with Etheline. He has a heart attack and dies at the age of 68. Chas accompanies him in the ambulance on the way to the hospital, and is the only witness to his death. The family attends his funeral together. Royal's epitaph reads that he "Died tragically rescuing his family from the wreckage of a destroyed sinking battleship."

Question: Who was suspicious of Margot?
Answer: Royal