Neptune founder Robin Geffen will continue to manage his range of funds after selling the fundhouse to Liontrust for £40m.
The sale of Neptune to Liontrust was confirmed by the latter in a stock market announcement this morning (July 31).
Mr Geffen founded Neptune in 2002 and was chief executive of the business as well as a fund manager.
He is lead manager on six funds, and will continue to run those at Liontrust while all of the other investment managers at Neptune will also transfer to Liontrust.
Neptune has assets under management of £2.8bn, meaning the combined firm will have assets of £17bn.
Neptune reported a profit of £996,000 for the year to the end of 2017, the most recent set of reported accounts.
In its most recent set of results, covering the year to March 2019, Liontrust reported a statutory profit of £19m.
Mr Geffen is not the only shareholder in Neptune, though he is the only shareholder listed at Companies House as a person of significant control, with a holding of between 25 and 50 per cent.
The sale of Neptune had been expected for some time, with Merian Global Investors also showing an interest to acquire the Hammersmith-based firm.
Neptune had been beset by a wave of staff exits in recent times, with head of sales Dan Lee exiting the business after less than a year in the role, and Ali Unwin leaving his role as US equity manager after a similarly short period.
There have been five US equity managers in just under two years.
Mr Geffen said: “It has been an easy decision to agree to sell Neptune to Liontrust. We have been hugely impressed by the excellent leadership and entrepreneurial attitude of the executive management team at Liontrust, the company's brand profile and by its sales and marketing capability.
"Neptune has great fund performance and an attractive investment proposition and will benefit hugely from the sales and marketing teams at Liontrust.
"The deal will also enable me to step away from managing the business and focus solely on managing funds and leading my investment team, which is my real passion. “
Jon Ions, chief executive of Liontrust, said: "Neptune is a great acquisition for Liontrust and will enhance our already excellent investment proposition in areas where there is strong demand such as global equities, equity income and emerging markets equities.
"We have created an environment to give fund management talent with robust and repeatable investment processes the best possible opportunity to deliver good, long-term returns for our clients.
"Robin and the rest of the team at Neptune will be able to focus on managing their funds and not be distracted by other day-to-day aspects of running a business.”