• It's official: T-Mobile and Sprint have announced plans to merge, with a combined company valued at $146 billion.

• John Legere, T-Mobile's CEO, is expected to serve in that role for the merged entity, which would retain the T-Mobile name.

• The agreement marks the culmination of four years of on-again, off-again discussions.

• The deal is likely to draw scrutiny from antitrust regulators, considering the Trump administration's treatment of AT&T and Time Warner's attempted merger.

• Sprint dropped by 13% in premarket trading on Monday, while T-Mobile slid 2.4%. Follow live trading on Markets Insider.

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The boards of T-Mobile and Sprint have put the finishing touches on a massive merger agreement that values a combined company at $146 billion.

T-Mobile's CEO, John Legere, made the announcement on Sunday by tweeting a seven-minute video breaking down the merger and linking to a website that further explains the combination.

Deutsche Telekom, which owns two-thirds of T-Mobile, would control the newly formed company.

Tweet Embed:
//twitter.com/mims/statuses/990622865522348035?ref_src=twsrc%5Etfw
I’m excited to announce that @TMobile & @Sprint
have reached an agreement to come together to form a new company – a larger, stronger competitor that will be a force for positive change for all US consumers and businesses! Watch this & click through for details.

Legere is expected to be the CEO of the combined entity, which would keep the T-Mobile name and have headquarters in Bellevue, Washington, and Overland Park, Kansas.

The deal, which would combine the third- and fourth-largest US wireless carriers, is expected to come under serious scrutiny from antitrust regulators, as the Trump administration has fervently opposed AT&T's proposed mega-acquisition of Time Warner.

The agreement marks the culmination of four years of on-again, off-again discussions between T-Mobile and Sprint; this is the third time the two rivals have tried to merge.

With a combined 127 million customers, the two firms are expected to compete directly with Verizon, the US's largest carrier, and AT&T.

"This isn't a case of going from four to three wireless companies — there are now at least seven or eight big competitors in this converging market," Legere said on Sunday.

The agreement involves T-Mobile exchanging 9.75 Sprint shares per unit of T-Mobile. Deutsche Telekom would own 42% of the combined company, while SoftBank, which controls 85% of Sprint, would own 27%. The public would hold the remaining 31%.