It's common advice to avoid using social media when driving, operating heavy machinery or engaged in other delicate tasks.

Now we can add to that list; don't tweet when handing out the world's most prestigious movie awards.

For the biggest disaster in the history of the Oscars went down when a starstruck accountant's mind could have been taken off the job after he spent the minutes before the Moonlight / La La Land mix-up tweeting pictures of celebrities from his personal account.

And Brian Cullinan, 57, the LA-based, Cornell-educated partner at PwC who was responsible for handing out the Best Picture award envelope, “feels very, very terrible and horrible” about the mistake, his boss has said.

The Wall Street Journal reports this morning on the existence of a now-deleted tweet bearing a photo of Emma Stone taken and sent by Cullinan, a mere three minutes before he made the biggest goof in Oscar history and gave Warren Beatty the wrong envelope on Sunday night.

“Best Actress Emma Stone Backstage!” Cullinan tweeted at 9:05 p.m. PST, according to the Wall Street Journal.

The newspaper obtained a copy of the post, along with multiple other tweets that he apparently sent out during the show, which suggest that the humble bean counter was not fully focused on the less-than-glamorous job of envelope-monitoring.

It was Cullinan’s fourth year handing out winner envelopes at the Academy Awards, according to Variety, which carries an interview today with PwC’s Tim Ryan, the accounting firm’s U.S. chairman and senior partner, who attributed the mistake to “human error.”

Ryan said he had spoken to Cullinan about the episode at length.

“He feels very, very terrible and horrible. He is very upset about this mistake. And as a firm, given that he is a partner of our firm, it is also my mistake and our mistake and we all feel very bad.”

Cullinan was positioned stage left during the evening. His colleague, Martha Ruiz, stood in the wings stage right, Ryan told Variety.

Each had a stack of envelopes for presenters entering from their side of the stage and then a pile of “backup” envelopes for the presenters entering from the other side of the stage at the Dolby Theatre.

The mistake happened after Cullinan pulled the lead actress envelope that was in the “backup” pile and handed it to Beatty.

“There’s a stack for the backups and he took from the wrong stack,” Ryan explained.

Ryan also moved to absolve Beatty and Dunaway, who have maintained their innocence, of blame, and, when asked if the presenters should have recognized the error, Ryan said: “No, look, it’s our job, not theirs.”

Ryan said that both envelope-handlers had prior knowledge of the contents of all the envelopes, and had memorized the winners as per company procedure.

Ryan said, “Martha (Ruiz)… immediately recognized that was not who won. She opened up her backup envelope to confirm her memory.”

Ryan said, he did not know why it took more than two minutes for the correction to be made, a time gap which led to the La La Land team taking to the stage and beginning their tearful acceptance speeches, before the movie's producer dramatically announced there had been a mistake and Moonlight had won.

Ryan told Variety that he had “reached out to the Academy and shared with them that we take full responsibility that Brian had made the mistake and the firm takes responsibility for that.”