Jeff Bezos bought Amazon stock for the first time in over 2 decades. He may be engaging in Elon Musk-style trolling.

• In a surprising move, Jeff Bezos bought a single share of Amazon for about $115 in late May.
• Bezos may have been engaging in some Elon Musk-style trolling, given the timing of the trade.
• The Amazon founder hasn't purchased shares of his company in over two decades, filings show.

Jeff Bezos unexpectedly bought a single Amazon share in late May, marking his first known purchase of the company's stock in over two decades. He may have been channeling Elon Musk and trolling Wall Street.

Amazon's billionaire founder and executive chair reported the May 25 trade to the Securities and Exchange Commission at 4.20 p.m. ET the next day. He also disclosed a gift of more than 69,000 shares to a non-profit in the same filing.

The bizarre single-share purchase, and the numbers implied by the reporting time and the stock donation — 4:20 and 69 — have fueled speculation that Bezos may have been mimicking rival Musk.

The Tesla and SpaceX chief has made plenty of playful references to the number "42" — a reference to Weed Day on April 20, and the answer to the "ultimate question of life, the universe and everything" in "A Hitchhiker's Guide to the Galaxy" — and "69" in recent years. For example, he initially offered to acquire Twitter for $42 billion last year, before sealing the deal at $44 billion.

Bezos paid $114.77 for his Amazon share. Subtract the shares he donated and his stake stood at 990,476,371 shares, worth $122 billion as of Friday's close. Amazon's stock price has climbed to $123.43 since then, meaning Bezos has made about $9 on the unusual investment.

Amazon stock has surged 47% this year, boosting the market capitalization of the e-commerce and cloud-services giant to $1.3 trillion. Bezos' roughly 990 million shares represent a nearly 10% stake in the company, and account for most of his $147 billion net worth, as estimated by the Bloomberg Billionaires Index.

Bezos' recent purchase is notable because he's overwhelmingly been a seller of Amazon stock over the past 20 years. Indeed, he's cashed out about $30 billion of stock to help finance his Blue Origin rocket company and fund other personal and business interests, per Bloomberg.

A broader rally of Big Tech stocks has lifted Amazon shares this year, as investors wager that the leading US tech companies will profit from the artificial-intelligence boom.

Bezos' stock purchase was disclosed in a SEC filing on May 26, but has attracted fresh attention in recent days following a Bloomberg report.