Katie Couric announced Thursday that she is mourning the loss of her mother and "best friend."

The 57-year-old journalist, who currently works as a Yahoo News Global Anchor, expressed her sadness Thursday morning on Twitter, writing, "My heart is broken. I lost my mom and best friend. We love you and miss you, Mom/Granny," along with a black and white photo of her late mother, Elinor H. Couric.

Couric, who co-anchored Today for 15 years, also posted a touching message on Facebook about her 91-year-old mother.

"She loved fiercely and was fiercely loved," she said.

Couric drew even closer to her mother when she began taking care of her in 2011, following the lost of her father to Parkinson's Disease.

Back in June, Elinor attended her daughter's wedding with John Molner in the Hamptons.

"It was so special that my mom could make the trip. She's 91. It was very moving," Couric told People magazine at the time. "I feel so lucky to be able to have her here." 

Despite her grieving, Couric went on to host the "Stand Up to Cancer" event held at the Dolby Theatre in Los Angeles on Friday.

"Mom was proud of @StandUpToCancer so I am here," she wrote on her Twitter Friday. "But my world and the world at large seems terribly off." 

Funding raised at the fourth biennial charity telecast will go towards cancer research. The event was broadcast on 32 stations and cable networks, including CBS, NBC, ABC, Fox, Showtime, HBO, ESPN, the National Geographic Channel, Bravo, ABC Family and VH1.

A number of A-list stars were expected to attend the event, including Robert Downey Jr., Reese Witherspoon, Jennifer Aniston, Halle Berry, Jon Hamm, Kiefer Sutherland, Ben Stiller, Kevin Bacon, Steve Carell, Sofia Vergara, Ben Stiller, Will Ferrell and Melissa McCarthy, reports CBS.

Viewers were also treated to performances from The Who, Jennifer Hudson, Lupe Fiasco & Common, Ariana Grande and Dave Matthews Band during the event.