In a deal that would combine the two largest cable operators, Comcast (CMCSA) is buying Time Warner Cable (TWC) for upward of $45 billion in stock.

CMCSA stock is down 2%. TWC stock is up nearly 8%.

The move was a surprise as Time Warner Cable was being sought after for months by smaller rival Charter Communications Inc.

With the two largest cable companies merging, insiders wondered whether the agreement would pass the scrutiny of anti-trust regulators (via Reuters).

The combined company would divest 3 million subscribers, about a quarter of Time Warner’s 12 million customers. Together with Comcast’s 22 million video subscribers, the roughly 30 million total would represent just under 30 percent of the U.S. pay television video market.

The new cable giant would tower over its closest video competitor, DirecTV, which has about 20 million video customers.

The merger would give some 23% of the newly merged company to TWC shareholders, though first must be approved by the U.S. Department of Justice and the Federal Communications Commission.

Smaller cable operator Charter was expected to be the company that took Time Warner. Charter offered $132.50 per share in a cash and stock deal last month — which Time Warner rejected as too low.

“Charter has always maintained that our greatest opportunity to create value for our shareholders is by executing our current business plan, and that we will continue to be disciplined in this and any other M & A activity we pursue,” Charter said in a statement Wednesday night.

The deal is expected to close by the end of the year.

The deal would be the second time in a year that the TV and media landscape is altered drastically by Comcast.

In 2013, Comcast bought NBC Universal for $17 billion.