Twitter's price for TellApart: $532 million

Twitter paid $532.6 million in stock for TellApart, an ad targeting company which it bought yesterday.

The deal was announced yesterday as part of Twitter's earnings call, but didn't immediately reveal the terms of the deal.

A new SEC filing reveals that Twitter offered 12.6 million shares at a price of $42.27, which was Twitter's share price at the end of a tumultuous trading day yesterday following poor earnings.

The stock dropped another 9% today, and ended at $38.49.

The actual number of shares will be determined after the deal closes, subject to a bunch of adjustments.

This may come as a surprise to people who weren't familiar with TellApart's business. But the company boasted of a $100 million run rate a couple years ago, so $500 million-plus seems like a reasonable deal.

The TellApart acquisition will let Twitter more effectively target ads at ever-more-specific groups of people across platforms, whether they're using phones or desktops, as well as TellApart's ad specialists.

Twitter CEO Dick Costolo was an angel investor in TellApart. However, Twitter says, "As an investor in TellApart, Dick was excluded from all board decisions about the acquisition to prevent any conflict of interest."