Facebook Vi ce President David Marcus stands down from his role at Coinbase.

Marcus will now focus on a mystery Facebook blockchain project.

A Coinbase representative has reportedly cited a “conflict of interest” as the reason for Marcus’ departure.

The rumour mill is in overdrive after a vice president of Facebook stood down from the board of directors at Coinbase, just seven months after he took the position.

According to Coindesk, David Marcus released a statement saying he resigned because of a new group he’s “setting up at Facebook around blockchain.”

This had led to all kinds of theories about what Facebook is planning, with some observers suggesting the social media giant could introduce a payments platform on its messaging app or even introduce its own cryptocurrency.

When Marcus joined the Coinbase in December last year, its CEO Brian Armstrong said Marcus would apply his expertise in the “payments and mobile space” to guide Coinbase in its overall mission.

“Getting to know Brian, who’s become a friend, and the whole Coinbase leadership team and board has been an immense privilege,” Marcus said in his statement.

“I’ve been thoroughly impressed by the talent and execution the team has demonstrated during my tenure, and I wish the team all the success it deserves going forward.”

According to Coindesk, a Coinbase spokesperson said Marcus’ decision to leave was made to avoid the appearance of a conflict of interest, but declined to elaborate.

Facebook is yet to comment.