WASHINGTON, D.C. -- Kara Kennedy Allen, daughter of the late Senator Edward M. Kennedy, died Friday night at a health club in Washington, D.C.

Kennedy Allen, 51, had just taken a swim in the club, according to multiple people on close terms with the Kennedy family, who said she was found in the steam room by another gym member.

The Washington, D.C., Metropolitan Police said they received a call shortly after 6 p.m. Friday night. Kennedy Allen had been working out at the Tenley Sport & Health Club, about a mile from her home in Northwest Washington. Police spokesman Hugh Carew said she was pronounced dead at the scene.

The cause was still undetermined, pending the results of an autopsy by the chief medical examiner in D.C., but the death did not appear suspicious, he said.

At the club this moring, a man behind a desk in the green marble lobby said, “Our hearts go out to the family.”

Declining to give his name, he said the club was not giving out details of the death in respect for the Kennedy family. “Right now we have no statement,” he said.

The oldest child of Edward and Joan Kennedy, Kennedy Allen was the mother of two teenagers, and had been married to Michael Allen, a professional sailor. She and Allen were divorced. Their daughter, Grace, turns 17 on Monday; their son, Max, is 14. Kennedy Allen had undergone surgery for lung cancer in 2003 and was reportedly in remission.

At Kennedy Allen’s home, a quaint, two-story brick and yellow stucco house on tree-lined Klingle Road, a few blocks from Washington National Cathedral, family members began gathering early this morning. Her brother Patrick Kennedy stood in the front yard, talking on a cellphone. Another man said her other brother, Edward Jr. Kennedy, was en route to D.C., while her stepmother, Victoria Reggie Kennedy, arrived this morning.

“It’s a devastating loss,” Patrick Kennedy said after ending his phone call.

“Right now we’re all about her kids, Maxie and Gracie. She was all about her kids, my sister,” he added, his voice cracking with emotion.

Commotion could be heard in the foyer of the house. A little girl with blonde hair looked out.

“We all know that she’s now with my dad,” Patrick Kennedy said before turning to head inside.

In a phone interview, Kara’s mother, Joan, recounted the time they spent together this past summer on Cape Cod.

“She stayed with me at my house in Hyannis Port all summer with her children,” Joan Kennedy told the Globe. “It was one of the most wonderful summers I’ve had, and Kara told me one of the best she’s had on the Cape.”

“We went swimming every day,” she added. “I’m so glad that her last summer was such a happy one.”

Joan Kennedy said she had been getting calls all day from Kennedy Allen’s cousins.

“It’s just such a shock because she was in such good health,” Joan Kennedy said. “She swam, I don’t know how many miles. She was in wonderful health.”

Word of her death rippled across a wide network of Kennedy family members and close confidants this afternoon.

“It is a shock,” said Scott Ferson, a former aide to her father, Senator Kennedy. “She had had health problems related to cancer, but not, as far as I know, heart disease. She took her health seriously, she ran a lot and was seemingly very healthy.”

The Rev. Mark R. Hession, the Kennedy family’s priest on Cape Cod, said he got to know Kennedy Allen when her father was suffering from cancer, and she and her children would celebrate Mass with him at the Kennedy family home in Hyannis Port.

“She was a great support to Ted, and the kids were, too,” Hession said, recalling how the children, during a blessing for health, would “go over to heir grandfather and rest their hands on him.”

“All of them helped to ease his suffering,” said Hession, who is pastor at Our Lady of Victory Parish in Centerville, where Kennedy Allen was married in 1990. “She was a wonderful woman, and a great parent, and an outstanding Christian. We’re all concerned for the wellbeing of her children now.”

The Edward M. Kennedy Institute for the United States Senate in Boston issued a statement that recalled Kennedy Allen as a “warm and caring person.”

“Her children were the light and joy of her life. Her magnificent strength in her successful battle with lung cancer was a quiet inspiration to all us and provided her family and fellow patients with hope,” the statement said.

Kennedy Allen recently co-produced a film for the institute, which was shown at its inaugural gala, according to the statement.

Kennedy Allen was diagnosed with lung cancer in 2002 and had a portion of her right lung removed at Brigham and Women’s Hospital in Boston in January 2003. She undertook a regimen of chemotherapy after her surgery and her cancer was thought to be in remission.

In a 2008 Globe story, she described her struggle with cancer and subsequent recovery, saying she was running five miles a day.

Active in family charities and philanthropic circles, Kennedy Allen kept a low public profile. She spoke at her father’s funeral service in 2009, and accepted the Medal of Freedom on his behalf during a ceremony with President Obama in the East Room of the White House later that year. This summer, she attended Patrick Kennedy’s wedding.

In addition to Patrick Kennedy, Kennedy Allen is survived by another brother, Edward M. Kennedy Jr., a Connecticut lawyer and advocate for the disabled.

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