For the second time this year, Dimensional Fund Advisors (DFA), the Austin-based investment management firm whose advisor-sold funds are often regarded as the original smart beta funds, has announced leadership changes at the top.

Co-CEO and Co-Chief Investment Officer Eduardo Repetto announced he is leaving the firm in September after 17 years and Gerard O’Reilly, currently co-CIO, will take his place in late September, also keeping both titles and serving alongside Co-CEO Dave Butler. DFA Founder David Booth, who’s also executive chairman of Dimensional, will continue in that role.

(Related: Butler to Replace Booth as Co-CEO of Dimensional Fund Advisors)

Booth commended Repetto for his “tremendous contributions” to the firm and O’Reilly’s work as a “vital member of its investments and senior management teams over the past 13 years.” O’Reilly will be added to the board of directors.

Booth also extolled the co-CEO model that the firm adopted in 2010 with Booth and Repetto at the helm. Booth gave up that role in February and became executive chairman. Dave Butler, head of Global Financial Advisor Services, retained that title and replaced Booth as co-CEO.

Neither Repetto nor DFA gave a reason for Repetto’s forthcoming departure, and there was no mention of the next stop for Repetto, who thanked his clients and fellow employees “that have enabled Dimensional to become this magnificent global business.”

The 36-year-old firm has $518 billion in assets under management and more than 1,100 employees operating in 12 offices in eight countries.

Morningstar analyst Alex Bryan says he doesn’t expect the latest executive changes at DFA will have a material effect on the firm but says it’s “never good to see two CEOs leave in one year.”

But only one of those CEOs is leaving the firm. Booth retains his title as executive chairman, and O’Reilly, who’s been with the firm since 2004, gets another promotion.

When the executive changes are completed, DFA will continue to keep investment expertise and client-facing expertise at the top, says Bryan referring to O’Reilly and Butler, respectively.

— Related on ThinkAdvisor: