After months of on again/off again talks, Anthem has agreed to buy Cigna in a $48.4 billion deal.

If the merger holds up to review by shareholders and regulators, it may put major control of the U.S. commercial health-insurance market in the hands of just three hulking players.

That’s because, a few weeks prior to the July 24 announcement, which was issued jointly and is being covered ubiquitously, Aetna agreed to acquire Humana.

If both transactions fly, three behemoths—the other being a loner but the largest by revenue, $154 billion UnitedHealth Group—will enjoy business power unimaginable in the health-insurance industry before the Affordable Care Act and other forces started reshaping U.S. healthcare economics.

It’s unlikely that either of the pending deals will quickly sail through to completion. Regulators at the Securities and Exchange Commission and elsewhere are expected to put through the wringer any combinations that concentrate so much control in so few boardrooms.

Meanwhile, Cigna shares were trading well below the offer price as of midday following the Friday-morning announcement. The Wall Street Journal reported this as a sign that investors are skeptical about the deal’s chances of survival.

All the same, in their joint announcement, the companies said they expect the transaction to close in the second half of 2016—and to save them nearly $2 billion a year after they pay $600 million in merger-related costs over the first two years.

“Anthem is confident in its ability to obtain all necessary regulatory and other approvals,” the companies said.

Including debt and other considerations, muliple sources reported, the deal rings up a total valuation of $54.2 billion.

“We believe that this transaction will allow us to enhance our competitive position,” added Joseph R. Swedish, the Anthem CEO who is set to head the combined entity, in prepared remarks, “and be better positioned to apply the insights and access of a broad network and dedicated local presence to the health care challenges of the increasingly diverse markets, membership and communities we serve.”

Forrester Research analyst Alex Cullen told the New York Times’s DealBook that the challenge facing all health insurers is moving from an insurance model focused on plans and claims to one centered on customer service.

“I would expect a lot of angst within Anthem management,” Cullen said, “on how to execute on a customer-centric strategy.”

Click here to read the joint announcement from Anthem and Cigna.