The co-hosts of "The Talk" have been revealing big secrets all week long -- and they saved the most shocking for last.

Sheryl Underwood left the audience stunned when she said she was actually born a twin, but her sister didn't make it. 

But that wasn't the shocking part. It's what Sheryl's mother told her about how her sister died that was really disturbing. Watch the clip above.

It sounds like Underwood has since repaired her relationship with her father -- and calls her sister her "guardian angel."

"I know she's here and every day I walk through that tunnel [to come on stage], she's coming with me," added Sheryl.

The reveal came after a week of secret spilling from the stars of the show.

On Thursday, Sara Gilbert said she started questioning her sexuality while dating Johnny Galecki -- and added she still struggles with it to this day. And earlier in the week, Aisha Tyler emotionally opened up about infertility and IVF treatment.

Julie Chen confirmed suspicions she had plastic surgery on Wednesday's show -- admitting she went under the knife after her former boss and an agent said she needed to look less Chinese.

And then there's Sharon Osbourne, whose biggest secret was that she hooked up with Jay Leno.