Carly Simon lost both her sisters to cancer this week.

The 78-year-old singer is grieving after Broadway composer Lucy Simon died following a battle with breast cancer just one day after former opera singer Joanna Simon lost her fight with thyroid cancer.

Both deaths - Lucy was 82, while Joanna was 85 - have been confirmed by a source close to Carly, although she has yet to comment publicly on the losses.

Carly, Lucy and Joanna were born in New York to parents Richard L Simon, founder of the Simon & Schuster publishing company, and his wife Andrea, a civil rights activist and singer. In the early 1960s, Lucy and Carly formed their own folk singing duo called The Simon Sisters.

The pair released the song Wynken, Blynken & Nod - which hit the Billboard top 100 - in 1964 before Lucy left showbiz to attend nursing school.

Carly Simon in her 1970s heyday. Photo / Getty Images

While they both went on to have solo careers, Lucy later enjoyed success as composer of the Broadway musical The Secret Garden in 1991, for which she earned a Tony nomination.

She went on to compose for the stage adaptation of Doctor Zhivago and HBO film The Positively True Adventures of the Alleged Texas Cheerleader-Murdering Mom.

Before her illness progressed, she had been working on On Cedar Street, a musical adaptation of the 2015 novel Our Souls At Night.

In 1962, Joanna made her debut at the New York City Opera as Mozart’s Cherubino, and went on to perform on stage with the New York Philharmonic, the Vienna Philharmonic, and the Pittsburgh Symphony Orchestra.

She went on to work as the arts correspondent for PBS’s MacNeil-Lehrer News Hour until 1992, and later worked in real estate. Lucy and Joanna were predeceased by their brother, photographer Peter Simon, who died of cardiac arrest at age 71 in 2018 after being treated for cancer.