By Sandra Gonzalez and Megan Thomas

CNN

LOS ANGELES (CNN) -- PricewaterhouseCoopers has taken "full responsibility" for the mistakes and "breaches of established protocols" that led to "La La Land" mistakenly being named best picture at the Oscars on Sunday night in one of the most infamous gaffes in the show's history.

In a statement released Monday evening, the firm confirmed that PwC managing partner Brian Cullinan "mistakenly handed the back-up envelope for Actress in a Leading Role instead of the envelope for Best Picture to presenters Warren Beatty and Faye Dunaway."

"Once the error occurred, protocols for correcting it were not followed through quickly enough by Mr. Cullinan or his partner," the statement said, referring to PwC employee Martha Ruiz.

"Moonlight" was eventually crowned best picture winner.

Ruiz and Cullinan were the two employees charged with managing the envelopes containing the names of Oscar winners. At the ceremony, Ruiz and Cullinan alternated handing envelopes to presenters from opposite sides of the stage.

PwC's statement added: "For the past 83 years, the Academy has entrusted PwC with the integrity of the awards process during the ceremony, and last night we failed the Academy."

The Academy also broke its silence on Monday evening.

In a statement, it apologized "to the entire cast and crew of 'La La Land' and 'Moonlight' whose experience was profoundly altered by [the] error."

"We salute the tremendous grace they displayed under the circumstances," the statement said. "To all involved --- including our presenters Warren Beatty and Faye Dunaway, the filmmakers, and our fans watching worldwide --- we apologize."

The Academy added: "We have spent last night and today investigating the circumstances, and will determine what actions are appropriate going forward. We are unwaveringly committed to upholding the integrity of the Oscars and the Academy of Motion Picture Arts and Sciences."

The statements come after revelations that Cullinan was tweeting shortly before the mistake was made.

At 9:05 p.m. on Sunday, Cullinan sent a now-deleted tweet from his personal account that showed fresh-off-the-stage winner Emma Stone smiling with her new Oscar in hand.

"Best Actress Emma Stone backstage! #PWC," Cullinan wrote.

The tweet is viewable in a cached page on Google.

The social media post came just minutes before Dunaway and Beatty were inadvertently given the envelope containing the already announced best actress results.

Cullinan has not responded to CNN's request for comment as of Monday evening.

PwC quickly apologized on Sunday night and said they were "investigating how this could have happened."

In the history of the Oscars, only one similar event has taken place.

Back in 1964, Sammy Davis Jr. was handed the wrong envelope when presenting the best musical score (adaptation or treatment) category and accidentally announced the winner for original musical score.

He corrected himself on stage after he was told he announced a winner who was not nominated in the category he was supposed to be presenting.

PwC has several measures in place meant to prevent such occurrences.

A 2016 Los Angeles Times story detailed one such precaution: the envelopes themselves. The names of the categories are printed on the outside to prevent confusion and the text used is "large enough for a presenter and cameras to read easily," the piece noted.

It's worth noting, however, that this year's envelope design was changed from gold paper with white labels to red paper with gold lettering -- considerably harder to read in dim backstage lighting.

To the cameras capturing the action on stage, the misstep was clear. Photos from Sunday, examined in detail in the hours after the show, confirmed that Dunaway and Beatty had the wrong envelope on stage.

Dunaway, who was the one to announce "La La Land" had won best picture, has declined to comment on the event.

After the envelopes are stuffed with the winners' names, they are sealed by the only two people who know the results ahead of the ceremony -- in this case, Ruiz and Cullinan. Two sets of winner-containing envelopes are made, and Ruiz and Cullinan are tasked with taking them to the ceremony, flanked by guards.

As an additional safety measure, Ruiz and Cullinan memorize the names of the winners. This is so they can be quick to respond in case the wrong name is read or share the winner with presenters in case something happens to the envelopes.

A 2013 Vanity Fair story recalled a time when Sharon Stone and Quincy Jones were tasked with presenting two awards back-to-back but accidentally gave the second envelope to the first winner. The PwC representative on hand was able to whisper the winner to Jones off stage.

Three "La La Land" producers spoke on stage before the error was announced to the Oscars audience.

"Moonlight" ended up winning three Oscars on Sunday night. "La La Land" earned five.