Elon Musk "has decided not to join" Twitter's board of directors, the social media company's CEO Parag Agrawal said late Sunday — days after it announced he would take a board seat.

Driving the news: Agrawal said in a memo shared to Twitter that Musk's appointment to the board was to become officially effective on Saturday. "Elon shared that same morning that he will no longer be joining the board. I believe this is for the best," he added.

Our thought bubble: Musk is still Twitter's largest shareholder. Had he taken a board seat, he would have been limited in how much of the company's shares he could own. This could be a prelude to him walking away, the start of a hostile takeover, or anything in between.

Flashback: Agrawal said last Tuesday that he was "excited" that Musk would join Twitter's board, after the Tesla CEO purchased a 9.2% stake in the company.

Between the lines: In the intervening days, Musk had been highly critical of Twitter.

• Musk suggested in a series of tweets Saturday night changes to the premium Twitter Blue service — including an authentication checkmark for all subscribers, cheaper subscription price, banning ads and offering the option to pay in cryptocurrency.
• The world's richest man also suggested turning Twitter's San Francisco HQ into a homeless shelter and openly questioned whether the microblogging service was dying.
• Musk even posed the question "Is Twitter dying?" noting many of the service's most-followed users post infrequently.

Worth noting: The SpaceX CEO told his 83 million-plus Twitter followers late last month that he was giving "serious thought" to building a social media platform to rival Twitter, which he criticized for "failing to adhere to free speech principles."

What to watch: Twitter had been due to host Musk for a staff "question-and-answer session" following his appointment to the microblogging site's board last week after he bought the Twitter shares, per the Washington Post.

• He's also been slated to give a TED talk Thursday morning in Vancouver, though it's unclear if that is still happening.
• A spokesperson for Twitter declined to comment on Musk's tweets.

What he's saying: Representatives for Musk could not immediately be reached for comment. But he tweeted several cryptic comments late Sunday — including one saying in "all fairness, your honor, my client was in goblin mode" and another stating: "Explains everything," per AP.

• Musk also tweeted a single face emoji with a hand over its mouth early Monday.

The intrigue: All of the tweets Musk posted about Twitter changes over the weekend and in the minutes following Agrawal's announcement appear to have been deleted.

Go deeper: Elon Musk could dictate the future of Twitter

Editor's note: This article has been updated with new details throughout.