UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington D.C. 20549

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FORM 8-K

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CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of report (date of earliest event reported): January 27, 2022

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FIRST INTERSTATE BANCSYSTEM, INC.

(Exact name of registrant as specified in its charter)

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(406) 255-5311

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 8.01. Other Events.

On January 27, 2022, First Interstate BancSystem, Inc. (“First Interstate”) issued a press release announcing that, upon the completion of the previously announced business combination transaction (the “Transaction”) of First Interstate and Great Western Bancorp, Inc. (“Great Western”) pursuant to the Agreement and Plan of Merger, dated as of September 15, 2021, by and between First Interstate and Great Western (the “Merger Agreement”), First Interstate expects that Scott Erkonen will join First Interstate and serve as the Chief Information Officer and Karlyn Knieriem will join First Interstate and serve as the Chief Risk Officer.

As previously announced, the Transaction is expected to close on or around February 1, 2022, subject to customary closing conditions set forth in the Merger Agreement.

A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

(d) Exhibits

Cautionary Note Regarding Forward Looking Statements

This communication contains “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Rule 175 promulgated thereunder, and Section 21E of the Securities Exchange Act of 1934, as amended, and Rule 3b-6 promulgated thereunder, which involve inherent risks and uncertainties. Any statements about First Interstate’s, Great Western’s or the combined company’s plans, objectives, expectations, strategies, beliefs, or future performance or events constitute forward-looking statements. Such statements are identified as those that include words or phrases such as “believes,” “expects,” “anticipates,” “plans,” “trend,” “objective,” “continue,” or similar expressions or future or conditional verbs such as “will,” “would,” “should,” “could,” “might,” “may,” or similar expressions. Forward-looking statements involve known and unknown risks, uncertainties, assumptions, estimates, and other important factors that change over time and could cause actual results to differ materially from any results, performance, or events expressed or implied by such forward-looking statements. Such forward-looking statements include but are not limited to statements about the benefits of the Transaction, including future financial and operating results, the combined company’s plans, objectives, expectations and intentions, and other statements that are not historical facts.

These forward-looking statements are subject to risks and uncertainties that may cause actual results to differ materially from those projected. In addition to factors previously disclosed in First Interstate’s and Great Western’s reports filed with the U.S. Securities and Exchange Commission (the “SEC”) and those identified elsewhere in this document, the following factors, among others, could cause actual results to differ materially from forward-looking statements or historical performance: the occurrence of any event, change, or other circumstance that could give rise to the right of one or both of the parties to terminate the Merger Agreement between First Interstate and Great Western; the outcome of any legal proceedings that may be instituted against First Interstate or Great Western; the possibility that the Transaction does not close when expected or at all because required conditions to closing are not received or satisfied on a timely basis or at all (and the risk that such approvals may result in the imposition of conditions that could adversely affect the combined company or the expected benefits of the Transaction); the risk that the benefits from the Transaction may not be fully realized or may take longer to realize than expected, including as a result of changes in, or problems arising from, general economic and market conditions, interest and exchange rates, monetary policy, laws and regulations and their enforcement, and the degree of competition in the geographic and business areas in which First Interstate and Great Western operate; the ability to promptly and effectively integrate the businesses of First Interstate and Great Western; the possibility that the Transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events; reputational risk and potential adverse reactions of First Interstate’s or Great Western’s customers, employees or other business partners, including those resulting from the announcement or completion of the Transaction; the dilution caused by First Interstate’s issuance of additional shares of its capital stock in connection with the Transaction; the diversion of management’s attention and time from ongoing business operations and opportunities on merger-related matters; and the impact of the global COVID-19 pandemic on First Interstate’s or Great Western’s businesses, the ability to complete the Transaction or any of the other foregoing risks.

These factors are not necessarily all of the factors that could cause First Interstate’s, Great Western’s or the combined company’s actual results, performance, or achievements to differ materially from those expressed in or implied by any of the forward-looking statements. Other unknown or unpredictable factors also could harm First Interstate’s, Great Western’s or the combined company’s results.

All forward-looking statements attributable to First Interstate, Great Western, or the combined company, or persons acting on First Interstate’s or Great Western’s behalf, are expressly qualified in their entirety by the cautionary statements set forth above. Forward-looking statements speak only as of the date they are made and First Interstate and Great Western do not undertake or assume any obligation to update publicly any of these statements to reflect actual results, new information or future events, changes in assumptions, or changes in other factors affecting forward-looking statements, except to the extent required by applicable law. If First Interstate or Great Western update one or more forward-looking statements, no inference should be drawn that First Interstate or Great Western will make additional updates with respect to those or other forward-looking statements. Further information regarding First Interstate, Great Western and factors which could affect the forward-looking statements contained herein can be found in the registration statement on Form S-4, as amended, as well as First Interstate’s Annual Report on Form 10-K for the fiscal year ended December 31, 2020, its Quarterly Reports on Form 10-Q, and its other filings with the SEC, and in Great Western’s Annual Report on Form 10-K for the fiscal year ended September 30, 2021, and its other filings with the SEC.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: January 27, 2022