Aegon UK has purchased Novia Investment Services from Novia Financial Holdings.
The purchase, subject to regulatory approval, will mean the development work on Aegon's platform, Aegon Retirement Choices, moves in-house as part of a drive towards becoming a fully digital business.
NISL was set-up as a separate company to build and administer the Aegon platform in 2011.
The original agreement gave Aegon a clause to purchase NISL and Aegon has decided to exercise this option.
All 40 staff at NISL will transfer to Aegon.
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Tommy Young, chief operating officer at Aegon UK, said: "We've been delighted with the success of the Aegon/Novia project.
"Moving the development work in-house is a very natural step in our progression, allowing us to take complete ownership of the entire platform as we continue to build a truly digital business."
Bill Vasilieff, chief executive of Novia Financial, said: "The project between Aegon and Novia has been an unqualified success for both businesses."