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A3 Capital
A3 Capital is the Belgian family office of Marnix Galle, managing wealth from Immobel real estate and Sioen Industries.
A3 Capital
General information
Firm type
Single Family Office
Year founded
—
AUM
Undisclosed
Location
Region
Europe
Country
Belgium
City
Brussels
Corporate office
Brussels, Belgium
Principals
Marnix Galle
Principal
Michèle Sioen
Family Member
Alfred Galle
Family Member
Sector focus
Frequently asked questions
Who runs investment decisions at A3 Capital?
Marnix Galle is the principal, and his wife Michèle Sioen is a family member involved through Sioen Industries. Investment decisions are made by the family; no external CIO or investment committee is publicly named (per Altss research).
How does A3 Capital source proprietary deal flow?
Deal flow is generated through Immobel's real estate development pipeline and Sioen Industries' industrial network. Marnix Galle's chairmanship of ULI Europe (2020–2022) also provides access to institutional real estate opportunities across Europe (per Altss research).
Is A3 Capital structured as a single family office or does it operate more like a venture firm?
It is a single family office. A3 Capital does not manage third-party capital. Its structure includes a STAK foundation for governance and Immobel Philanthropy as a separate charitable vehicle, typical of European multi-generational family offices (per Altss research).
Does A3 Capital participate in fund commitments or only direct deals?
The office primarily holds direct assets — real estate projects via Immobel and the Four Seasons Marbella resort. It also supports Madaster, a circular economy startup, through an Immobel partnership. No fund commitments are publicly documented (per Altss research).
What investment stages does A3 Capital typically target?
Its holdings are predominantly in mature, income-generating assets: mixed-use real estate developments, hospitality assets like the Four Seasons Marbella, and established industrial businesses through Sioen Industries. Direct startup investments appear limited to corporate partnerships like Madaster (per Altss research).
Where does the underlying wealth come from?
Wealth originated from two sources: Marnix Galle's stake in Immobel, a public real estate developer founded by the Galle family, and Michèle Sioen's leadership of Sioen Industries, a textile and chemicals manufacturer. The Sioen family founded Sioen Industries; the Galle family built Immobel (per Altss research).
Does A3 Capital maintain philanthropic structures, and how are they separated?
Yes. Immobel Philanthropy is the charitable arm, separate from the investment portfolio. The office also uses a STAK (Stichting Administratiekantoor) foundation for governance, a Dutch legal structure that separates voting rights from economic ownership, common in European family offices (per Altss research).
Profile maintained by Altss using OSINT (open-source intelligence), regulatory filings, licensed data partners, and verified direct submissions. Read the methodology. Last updated: . Continuous refresh with full update cycles at least every 30 days.
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