ABC News’ TJ Winick reports:

She bore that famous last name –  still, Kara Kennedy lived her life outside the spotlight as much as any Kennedy could.

Friday night, that life ended at just 51 when Kara Kennedy suffered a heart attack after working out at a gym in Northwest Washington, D.C.

“She’s with dad,” brother and former Congressman Patrick Kennedy told the Associated Press.

She was a mother of two teenagers, Grace and Max.

She was known for her fighting spirit – she beat inoperable lung cancer in 2002.

Five years later, her mother told the Boston Globe Kara Kennedy was cancer free and running five miles a day.

“Last summer she was in the best health that I can remember,” mother Joan Kennedy said.

Even so, the cancer treatment “took quite a toll on her and weakened her physically,” Patrick Kennedy said, “Her heart gave out.”

In August 2009, with her father Senator Ted Kennedy on his deathbed, Kara Kennedy accepted the Presidential Medal of Honor on his behalf.

Kara Kennedy was not the only member of her immediate family to battle cancer.

Her father Ted died of a malignant brain tumor and her brother Ted Jr. beat bone cancer though he lost a leg to the disease when he was just 12.

She is just the latest Kennedy to die young in an extended family that has suffered immeasurable loss.

“It is an unlucky family in a lot of ways and of course we pay a lot more attention to them because it is such a prominent family,” said Kennedy biographer Susan Milligan.

Uncles Robert and JFK were assassinated.

Her cousin David was just 28 when he died of a drug overdose.

Her cousin Michael was 39 years old when killed in a skiing accident.

And, of course, cousin John, Jr. was only 38 when the small plane he was piloting crashed into the Atlantic.

“People assume that when you come from a family like that with a lot of wealth and privilege that your life is charmed and it is not,” Milligan said.

Funeral arrangements for Kara Kennedy right now are still being organized.