425

Filed by: Westar Energy, Inc.

pursuant to Rule 425 under the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

under the Securities Exchange Act of 1934

Subject Company: Westar Energy, Inc.

Commission File Number: 001-03523

Date: September 22, 2016

{The following is an electronic message from Mark Ruelle, President and Chief Executive Officer of Westar Energy, Inc., to employees.}

Merger update

At recent employee meetings throughout the company, management discussed the “checklist” of regulatory items we must complete prior to closing the proposed transaction. One of those items is to make a filing with the Department of Justice related to what’s referred to as the Hart-Scott-Rodino Act waiting period. It requires companies to give federal authorities notice and time to review proposed business combinations. The Department of Justice staff indicated to us that we could make the filing, and we expect to do so in the next few days. Then, if within 30 days no action has been taken on the filing, that particular regulatory obstacle will be behind us.

In addition, today we settled the lawsuits filed by parties objecting to the transaction. As we shared earlier, it is common to have someone file a lawsuit when mergers are announced. We were able to settle those lawsuits by simply modifying some of the language in the bidding documents. With that, the litigants agreed to stand down.

We will continue to share merger process updates as additional information becomes available.

Important Information for Investors and Shareholders

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval. In connection with the proposed transaction between Westar Energy, Inc. (“Westar Energy”) and Great Plains Energy Incorporated (“Great Plains”) on July 14, 2016, Great Plains filed with the Securities and Exchange Commission (“SEC”) a registration statement on Form S-4 that included a preliminary joint proxy statement of Great Plains and Westar Energy that also constitutes a prospectus of Great Plains. The registration statement was declared effective by the SEC on August 19, 2016, and Great Plains and Westar Energy commenced mailing the definitive joint proxy statement/prospectus to their respective shareholders on or about August 26, 2016. This material is not a substitute for the joint proxy statement/prospectus or registration statement or for any other document that Great Plains or Westar Energy may file with the SEC and send to Great Plains’ and/or Westar Energy’s shareholders in connection with the proposed transactions. INVESTORS AND SECURITY HOLDERS OF GREAT PLAINS AND WESTAR ENERGY ARE URGED TO READ THE PROXY STATEMENT/PROSPECTUS AND OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY BECAUSE THEY CONTAIN IMPORTANT INFORMATION. Investors and security holders can


obtain free copies of the proxy statement/prospectus and other documents filed with the SEC by Great Plains or Westar Energy through the website maintained by the SEC at http://www.sec.gov. Copies of the documents filed with the SEC by Great Plains are available free of charge on Great Plains’ website at www.greatplains.com, in the “Investor Relations” tab near the bottom of the page, or by contacting Great Plains’ Investor Relations Department at 1-800-245-5275. Copies of the documents filed with the SEC by Westar Energy are available free of charge on Westar Energy’s website at www.westarenergy.com or by contacting Westar Energy’s Investor Relations Department at 785-575-8227.

Great Plains and Westar Energy and their respective directors and certain of their respective executive officers may be considered participants in the solicitation of proxies with respect to the proposed transactions under the rules of the SEC. Information about the directors and executive officers of Great Plains may be found in its 2015 Annual Report on Form 10-K filed with the SEC on February 24, 2016, and definitive proxy statement relating to its 2016 Annual Meeting of Shareholders filed with the SEC on March 24, 2016. Information about the directors and executive officers of Westar Energy may be found in its 2015 Annual Report on Form 10-K filed with the SEC on February 24, 2016, and definitive proxy statement relating to its 2016 Annual Meeting of Shareholders filed with the SEC on April 1, 2016. These documents can be obtained free of charge from the sources indicated above. Additional information regarding the participants in the proxy solicitations and a description of their direct and indirect interests, by security holdings or otherwise, are included in the joint proxy statement/prospectus that is filed with the SEC.

Forward Looking Statements

This communication contains certain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 in connection with the proposed merger of Great Plains and Westar Energy. These statements include statements regarding describe nature of future statements, e.g. the anticipated closing date of the transaction or anticipated future results. Forward-looking statements may include words like “believe,” “anticipate,” “target,” “expect,” “pro forma,” “estimate,” “intend,” “guidance” or words of similar meaning. Forward-looking statements describe future plans, objectives, expectations or goals. Although Great Plains and Westar Energy believes that these statements are based on reasonable assumptions, all forward-looking statements involve risk and uncertainty. The factors that could cause actual results to differ materially from these forward-looking statements include those discussed herein as well as, without limitation, delays in completing the merger, including as a result of delays in obtaining regulatory approval or shareholder approval, changes in general economic conditions and regulatory and legislative changes that adversely affect the business in which Great Plains and Westar Energy are engaged. These forward looking statements speak only as of the date of this communication, and Great Plains and Westar Energy expressly disclaim any obligation or undertaking to disseminate any updates or revisions to any forward-looking statement contained herein to reflect any change in Great Plains’ or Westar Energy’s expectations with regard thereto or any change in events, conditions or circumstances on which any such statement is based. Please refer to the publicly filed documents of Great Plains and Westar Energy, including the most recent Forms 10-K and 10-Q, for additional information about Great Plains and Westar Energy and about the risks and uncertainties related to the business of each of Great Plains and Westar Energy which may affect the statements made in this communication.