Weeks after her husband died, Sheryl Sandberg received this letter.

Sheryl Sandberg was deep in grief after her husband’s death when she received a letter that seemed to confirm her worst fears.

Speaking to close friend Katie Couric about her new book, ‘Option B’, Sandberg described the moment she received the unnerving letter.

It was just a few weeks after ‘Lean In’ author’s husband, Dave Goldberg, had died suddenly of a cardiac arrhythmia after collapsing at a hotel gym while on holiday in Mexico in May 2015.

Listen: Sometimes, it’s beneficial to structure our grief.

“A lot of people kept saying ‘it gets better’, but it didn’t feel like it would ever get better,” the mum-of-two told Couric during an interview for her podcast.

“I felt like there’s a void closing in on me.”

Sandberg described the “overwhelming” grief that made her feel as if she wasn’t going to be able to live through another minute, let alone a day or a week.

Feeling like the pain might never subside, she opened a letter from a woman who shared a devastating message.

It read, “I wish I had something to say to you, but I don’t – because it’s been years and it really doesn’t get much easier. And a friend of mine lost her husband 10 years ago and it doesn’t get easier.”

Sheryl said that she was "not strong enough to read that letter".

Devastated and fearing that the woman's message might be true, Sandberg called Couric and friend, psychologist Adam Grant.

Couric, who lost her own husband, Jay Monohan, 19 years ago, said she immediately told her friend the woman was wrong and "unhelpful".

Despite its disconcerting effect, the 47-year-old said she was still grateful to have received the letter because she "learned something important after that".

That important lesson came from Grant, who flew interstate to visit Sheryl to tell her in person that it wasn't true.

A post shared by Sheryl Sandberg (@sherylsandberg) on Apr 23, 2017 at 5:45pm PDT

"I think the main thing that I said to Sheryl was 'look that does not have to be your experience'."

Grant told Sandberg she had a choice: she could suffer for decades like some others do, or she could build resilience - for herself, but also for her children.

It was that conversation, along with a viral Facebook post Sandberg wrote about her grief, that was the genesis for 'Option B', which she co-wrote with Grant.

Did someone tell you something particularly unhelpful after you lost a loved one?