Mistras Group, Inc.: 5%+ holders

As of November 6, 2026, 5 holders' latest Schedule 13D or 13G filings report owning 5% or more of Mistras Group, Inc. The largest reported stake is Aspasia Felice Vahaviolos', at 19.2%. 15 filings are on record since July 15, 2025 (Schedule 13G/A, August 13, 2026).

Mill Road Capital III, L.P. also filed stake reports on 2 other companies ↓

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Key facts

• Filing 2026-10-07 · Reporting person: Stephanie Athena Foglia · Sole voting: 1,608,595 · Shared voting: 3,923,718 · Sole dispositive: 1,608,595 · Shared dispositive: 3,923,718 · SCHEDULE 13D/A, 2026-10-07
• Filed 2026-09-21 · Holder: Stephanie Athena Foglia · Percent: 19.1% · SCHEDULE 13D/A
• Filing 2026-09-18 · Reporting person: Mill Road Capital III, L.P. · Sole voting: 1,938,316 · Shared voting: 0 · Sole dispositive: 1,938,316 · Shared dispositive: 0 · SCHEDULE 13D/A, 2026-09-18
• Filed 2026-09-14 · Holder: Stephanie Athena Foglia · Percent: 17.4% · SCHEDULE 13D/A
• Filing 2026-08-13 · Reporting person: Aspasia Felice Vahaviolos · Sole voting: 1,794,839 · Shared voting: 4,310,811 · Sole dispositive: 1,794,839 · Shared dispositive: 4,310,811 · SCHEDULE 13G/A, 2026-08-13

Mistras Group, Inc. has 15 Schedule 13D or 13G filings on record since 2025-07-15. 5 holders' latest filing reports 5% or more of common stock, $0.01 par value. Each figure below is the holder's own, as filed, with the filing linked.

Holders

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More on Mistras Group, Inc. and the records around it.

Mistras Group, Inc. elsewhere on the record

• Who owns it

Companies that share a holder

• Mill Road Capital III, L.P. also filed stake reports on 2 other companies: Alta Equipment Group Inc. (Jan 2026), Landsea Homes Corporation (Jul 2025)
• Dimensional Fund Advisors LP also filed stake reports on 366 other companies: Acadia Healthcare Co Inc (Oct 2026), ADT Inc (Oct 2026), AGCO Corp (Oct 2026)

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What the Full Report on Mistras Group, Inc. covers

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2. Which Company This Is

3. What They Do, And How The Money Works

4. Who Runs It, And How To Reach Them

5. The Money: Funding, Valuation, Runway

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7. Warning Bells

8. Sources

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Voting and dispositive power, as filed

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The latest filing identifies Mistras Group, Inc. by CUSIP 60649T107 and gives its principal executive office as 195 CLARKSVILLE ROAD, PRINCETON JUNCTION, NJ 08550 (SCHEDULE 13D/A, 2026-10-07).

What the percentages are based on

19.2* * This percentage calculation is based on 31,849,893 outstanding shares as of August 5, 2026 as reported by the issuer.Aspasia Felice Vahaviolos, SCHEDULE 13G/A, 2026-08-13

Source of funds (Item 3)

The Trust was established by its grantor, Aspasia F. Vahaviolos. The shares held by the Trust were acquired by a gift from Ms. Vahaviolos, and Ms. Foglia is the trustee for the Trust. The shares beneficially owned by Ms. Vahaviolos were acquired as described in her previous filings on Schedule 13G, and consist of 2,154,541 shares held directly by Ms. Vahaviolos and 3,923,718 shares held by the Trust. Ms. Foglia directly owns 2,000 shares purchased for cash in the Issuer's initial public offering and holds 12,663 shares received as compensation for employment with the Issuer.Stephanie Athena Foglia, SCHEDULE 13D/A, 2026-10-07

Item 3 of the Schedule 13D shall hereby be amended and restated in its entirety as follows: The Reporting Persons have acquired beneficial ownership of an aggregate of 1,938,316 shares of Common Stock for $13,897,120 using working capital from the Fund and the proceeds of margin loans under margin loan facilities maintained in the ordinary course of business by the Fund with a broker on customary terms and conditions.Mill Road Capital III, L.P., SCHEDULE 13D/A, 2026-09-18

Purpose of Transaction (Item 4)

Stephanie Athena Foglia

Item 4 of the Schedule 13D is hereby amended and restated in its entirety as follows: On September 17, 2026, the Issuer entered into an Agreement and Plan of Merger (the "Merger Agreement") with Athena Purchaser, LLC ("Parent") and Athena Merger Sub, Inc., a wholly owned subsidiary of Parent ("Merger Sub"). The Merger Agreement provides that, upon the terms and subject to the conditions set forth therein, Merger Sub will merge with and into the Issuer, with the Issuer surviving the merger as a wholly owned subsidiary of Parent (the "Merger"). At the effective time of the Merger (the "Effective Time"), each share of common stock, par value $0.01 per share, of the Issuer ("Common Stock") issued and outstanding immediately prior to the Effective Time (other than shares held by Parent, Merger Sub or the Issuer as treasury stock, and shares held by stockholders who properly exercise and perfect appraisal rights under Section 262 of the General Corporation Law of the State of Delaware) will be cancelled and converted into the right to receive $20.35 per share in cash, without interest and subject to any applicable withholding taxes (the "Merger Consideration"). Concurrently with the execution of the Merger Agreement, each Reporting Person entered into a voting and support agreement (each, a "Voting Agreement" and collectively, the "Voting Agreements") with Parent, pursuant to which the Reporting Persons agreed, among other things, to vote their shares of Common Stock in favor of …The first part of Item 4 of the SCHEDULE 13D/A filed 2026-10-07; the filing has the rest

Timeline

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Questions about who owns Mistras Group, Inc.

Who owns Mistras Group, Inc.?

On this page, 5 holders' latest ownership filings report 5% or more of Mistras Group, Inc.: Aspasia Felice Vahaviolos (19.2%, Schedule 13G/A, filed 2026-08-13), Stephanie Athena Foglia (19.1%, Schedule 13D/A, filed 2026-10-07), Mill Road Capital III, L.P. (6.1%, Schedule 13D/A, filed 2026-09-18), Dimensional Fund Advisors LP (5.2%, Schedule 13G, filed 2025-07-15) and Kristy Kyriakopoulos (5.12%, Schedule 13G/A, filed 2026-03-31).

Who are the largest shareholders of Mistras Group, Inc.?

By the share each holder's latest filing reports, the largest holders of Mistras Group, Inc. on this page are Aspasia Felice Vahaviolos (19.2%), Stephanie Athena Foglia (19.1%) and Mill Road Capital III, L.P. (6.1%).

When did Aspasia Felice Vahaviolos buy into Mistras Group, Inc.?

The filings give report dates, not purchase dates. The earliest filing from Aspasia Felice Vahaviolos on this page is the Schedule 13G/A, filed 2026-08-13, reporting 19.2%. That earliest filing is itself an amendment, which updates an earlier report.

Is this an audit or a full list?

Neither. The ownership list on this page covers only Schedule 13D and 13G filings, which holders make once they own 5% or more of a class of shares (an amendment can report a stake that has since fallen below 5%); 15 such filings are shown here. It is not an audit and not a full cap table: holders who never reached 5% are not listed, and a stake can change after its latest filing.

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Where this comes from

Anyone who comes to own more than 5% of a class of a listed company's voting shares has to tell the SEC. A holder who may seek to change or influence the company files Schedule 13D, and has to say in Item 4, "Purpose of Transaction", what it intends to do. A holder with no such intent, such as many index and passive funds, may file the shorter Schedule 13G. Both are amended when the stake changes, including when it falls below 5%.

Every row here is one of those filings, linked to the filing itself. Percentages and share counts are exactly as the holder filed them, for the holder the filing names; an amendment showing a lower figure is shown as filed. Item 4 text is quoted word for word. Where a 13D's Item 4 contains a sentence stating a definite intent to influence the company, that sentence is marked and quoted; the page does not describe the holder or its motives beyond the words it filed. Nothing here is investment advice.

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