A daughter of billionaire shopping mall magnate Melvin Simon claims her late father was coerced into approving a new estate plan that increased the amount of his fortune going to her stepmother by hundreds of millions of dollars.Deborah Simon filed a will contest Thursday in Hamilton County Superior Court. She claims her father couldn't sign a new agreement himself."In fact, Melvin was so ill that he was unable to sign either his new will or trust agreement himself, necessitating someone to hold a pen in Melvin's hand and move his hand as he allegedly `signed' both documents," the complaint reads.Mel Simon was the founder of Simon Property Group Inc. and co-owner of the Indiana Pacers. He died Sept. 16 at age 82.The filing was first reported by the Indianapolis Business Journal.Mel Simon had been married to Bren, his second wife, since 1972. Deborah Simon is one of Mel's children from his first marriage. His first wife, Bess Meshulam Simon, died of cancer in 1977.A message seeking comment left Saturday with Bren Simon's lawyer was not immediately returned.Mel Simon's philanthropy included $50 million for Indiana University's cancer center and $10 million to the Indianapolis Museum of Art, along with support for other health care and arts-related projects.Simon, who was the son of a Bronx tailor, arrived in Indianapolis in the 1950s while in the Army and entered the commercial real estate business in the city after his discharge.The business he started in 1960 as Melvin Simon & Associates grew into the country's largest shopping mall company, with ownership interest in more than 300 properties in the United States, Europe and Japan.Forbes magazine estimated Simon's fortune last year at $1.3 billion.