BREAKING: Dianne Feinstein dead at 90

Senator Dianne Feinstein of California has died at the age of 90, two sources familiar with the matter told NBC News.

Feinstein was the longest-serving female senator and longest-serving senator from California. She had announced plans to retire in February after the end of her term, which would have ended at the beginning of 2025.

In a statement after Feinstein announced her retirement, Biden said "Over the three decades I’ve known her, Dianne and her late husband Richard became dear friends to Jill and me. I’ve served with more US Senators than just about anyone. I can honestly say that Dianne Feinstein is one of the very best."

With Feinstein’s death, the Seventeenth Amendment "allows state legislatures to empower the governor to appoint a replacement to complete the term or to hold office until a special election can take place," meaning California Governor Gavin Newsom would be in charge of issuing a replacement for Feinstein.

In a statement, Biden said that Feinstein was a "pioneering American. A true trailblazer. And for Jill and me, a cherished friend."

"In San Francisco, she showed enormous poise and courage in the wake of tragedy, and became a powerful voice for American values. Serving in the Senate together for more than 15 years, I had a front row seat to what Dianne was able to accomplish."

Biden later added, "As we mourn with her daughter Katherine and the Feinstein family, her team in the Senate, and the people of California, we take comfort that Dianne is reunited again with her beloved Richard. May God Bless Dianne Feinstein."

James Sauls, Feinstein’s chief of staff, said, "Sadly, Senator Feinstein passed away last night at her home in Washington, DC. Her passing is a great loss for so many, from those who loved and cared for her to the people of California that she dedicated her life to serving."

"She left a legacy that is undeniable and extraordinary. There is much to say about who she was and what she did, but for now, we are going to grieve the passing of our beloved boss, mentor and friend."

According to USA Today, Feinstein was present in the Senate on Thursday, casting a vote at 11:45 am. She was not present for two votes held later in the afternoon.

At 5:21 pm on Thursday, her official X account issued a post slamming Azerbaijan for the forcing out of Christian Armenians in the Nagorno-Karabakh region.

Feinstein’s website lists among her "most notable achievements" as the enactment of the 1994 Assault Weapons Ban, and the "six-year review of the CIA’s detention and interrogation program that culminated in the 2014 release of the report’s executive summary and passage of legislation ensuring that certain post-9/11 interrogation methods are never used again."

"Senator Feinstein’s career has been one of firsts. She was the first woman president of the San Francisco Board of Supervisors, the first woman mayor of San Francisco, the first woman elected Senator of California, the first woman member and first woman ranking member of the Senate Judiciary Committee, the first woman to chair the Senate Rules and Administration Committee and the first woman to chair the Senate Intelligence Committee," the website states.

Fox News was told that members of her staff have placed flowers on Feinstein’s desk on the Senate floor as of Friday morning.

Feinstein was hospitalized in August after tripping in her home, but was released later that night. Shortly before the fall, Feinstein gave power of attorney to her daughter.

Lawmakers have raised concerns over her fitness to remain in Congress, with the lawmaker suffering from extensive health issues for more than a year.

Feinstein had been absent from the Senate for around three months earlier this year because of shingles and complications related to the virus. Her office revealed when she returned to office in May that she was suffering from encephalitis, or swelling of the brain, and Ramsay Hunt Syndrome, which can cause facial paralysis and hearing loss.

This is a breaking story and will be updated.