Former First Lady Nancy Reagan has died at her home in Los Angeles on Sunday morning, according to ABC News. She was 94.

The reported cause of death was congestive heart failure, according to a representative, Joanne Drake, in a statement reported by ABC News:

"Mrs. Reagan will be buried at the Ronald Reagan Presidential Library in Simi Valley, California, next to her husband, Ronald Wilson Reagan, who died on June 5, 2004."

Reagan was known for her fierce loyalty to her husband, former President Ronald Reagan. After standing behind him while he battled Alzheimer's in the final years of his life, she also advocated for stem cell research to learn more about the disease. The former first lady faced health challenges of her own, being diagnosed with breast cancer in 1987 and undergoing a mastectomy.

Jeffrey Lord, former Reagan administration White House Political Director, told CNN early Sunday that she was seriously protective of her husband, describing her as "the enforcer" and "tough." She cared for Ronald Reagan until he died on June 5, 2004 and explained this loyalty in a 1998 Vanity Fair article, where she stated: "When I say my life began with Ronnie, well, it's true. It did."

In her role as first lady, Nancy Reagan advocated to decrease drug and alcohol abuse among Americans in the "Just Say No" campaign. The anti-drug message became a television campaign, along with a program in schools, which many argued was too simplistic in addressing the real nature of addiction.

The former first lady was also an actress who appeared in movies and married Ronald Reagan in 1952, who was then an actor as well as the president of the Screen Actors Guild.

Her family, including her step-son, began to respond to her death early Sunday: