Apollo Global Management Inc. agreed to acquire Athene Holding Ltd. in an all-stock deal that values the annuity business at about $11 billion.

The deal is expected to close in January 2022, the companies said in a statement. Apollo was already the annuity seller’s biggest shareholder, with the firm and related entities owning a 35% stake.

It’s a move that combines two businesses providing products and services in high demand — investment returns and retirement income, the firms said in the statement. The deal is “substantially accretive,” more than doubling Apollo’s reported earnings last year, they said.

The private equity firm established Athene in 2009, and has built it into one of the top fixed-annuity providers in the U.S. In 2016, the insurance firm raised just over $1 billion in an initial public offering. Athene has become an essential fixture in Apollo’s financial apparatus, and private equity rivals have since sought to build up their own insurance businesses.

“This merger is all about alignment between Apollo and Athene, amongst Apollo’s stockholders and with our limited partners,” Marc Rowan, an Apollo co-founder and its incoming chief executive officer, said in the statement. “For Apollo and Athene, we will have total alignment to optimize our strategy and allocate capital efficiently.”

Monday’s surprise announcement came weeks after Apollo unveiled a major overhaul, with co-founder Leon Black relinquishing his CEO post no later than July amid fallout over his business ties to Jeffrey Epstein.

As part of the changes, the firm also said it would have more independent directors and convert to a new stock structure with just one class of voting rights.

Athene was perhaps Rowan’s greatest triumph for Apollo. Taking a page from Warren Buffett’s play book, he devised the insurance company to throw off vast sums that Apollo could then use for investments. Athene is one reason that Apollo today is the envy of the private equity business.

Under the terms of the deal, each Athene common share will be exchanged for 1.149 shares of Apollo common stock, with Apollo shareholders owning about 76% of the combined company once the transaction is completed.

In 2019, the two deepened their ties with further investments in each other. The insurer allows the private equity firm to collect money from annuity holders — what’s known as “permanent capital” — and invest the assets in the credit funds, distressed debt and buyouts for which Apollo is better known.

Athene CEO Jim Belardi has said that his business, after generating record growth last year, was focusing on large, complex transactions.

“We have a track record of those kinds of deals, and we like our chances,” Belardi said last month. “We want people knocking on our doors.”

The combined company will be led by Rowan, while Athene will continue to be led by Belardi and his current management team. Four Athene directors will join the combined company’s board, including Belardi.

Apollo also said Monday it plans to convert to a full C-corp, with a one-share, one-vote structure by January, and that the deal will allow the stock to be eligible for inclusion in more market indexes, including the S&P 500.