The U.S. Securities and Exchange Commission on Friday confirmed that it is investigating Elon Musk's early April disclosure of an ownership stake in Twitter, which came ahead of his agreement to acquire the company.

Driving the news: At is issue is the question of why Musk seemingly disclosed his 9.2% position in Twitter after he was legally required to do so, and if that disclosure was still faulty.

It's important to note that the SEC's letter came on the same day as Musk's disclosure, which is before he offered to buy Twitter outright.

Background: Musk and the SEC have tussled before, over his false claim about having "funding secured" to take Tesla private, but that mostly resulted in a slap on the wrist, which Musk remains sore over.

Other developments: Musk this week disclosed that he plans to front all $33.5 billion of equity he committed to the deal, as he allowed a $12.5 billion margin loan to lapse (thus boosting Tesla stock). No word yet on if he's secured additional investment partners, although talks appear to be ongoing with Jack Dorsey and others.

Final numbers: Twitter stock opened trading on Friday at $39.57 per share, a 27% discount to Musk's takeover price.