Dick Grasso is no longer persona non grata at the New York Stock Exchange.

NYSE Euronext (NYX) chief executive Duncan Niederauer has extended an invitation to Grasso to attend the Big Board’s commemoration of the 10-year anniversary of the Sept. 11 terrorist attacks, sources tell FOX Business.

Grasso was chief executive of the exchange at the time of the attacks and was a leading figure in getting the financial markets ramped up again days later.

But he was forced out of the NYSE in 2003 amid controversy over the size of his pay and retirement package.

Because of the controversy, subsequent chief executives, including Niederauer and John Thain, have pointedly kept Grasso out of major events. But the invitation comes as Niederauer is trying to build support for the NYSE’s takeover by Germany’s Deutsche Boerse. Niederauer has been seeking allies to avoid having to meet officials from the Nasdaq (NDAQ), which has made a counterbid and is in the process of planning a tender offer directly to NYSE shareholders as early as next week, as reported first by FOX Business.

Grasso was not immediately available for comment and an NYSE spokesman had no comment, but the former NYSE chief was said to be "touched" by the overture, and will likely attend. Niederauer and Grasso had often butted heads while Grasso was NYSE and Niederauer was a Goldman Sachs (GS) executive pushing electronic trading over the specialist-based system that Grasso favored. But after the NYSE announced its planned hook up with the Deutsche Boerse several weeks ago, Grasso had made some positive comments, prompting a call from Niederauer, the first time the two had spoken in years.

Grasso has remained more neutral in television interviews with FOX Business as the Nasdaq and IntercontinentalExchange (ICE) have offered their higher rival bid.

The olive branch comes after years of bitterness between Grasso and the NYSE management. Soon after Grasso was ousted in 2003, new NYSE management, under former chairman John Reed, issued a report critical of how Grasso received his compensation; Grasso was then sued on behalf of the exchange by then-New York Attorney General Eliot Spitzer, who wanted the return of as much as $140 million in compensation.

Ultimately, Grasso was ordered by a state Supreme Court judge to pay back much of his pay, but that was reversed on appeal after a higher court found that the case lacked standing because the NYSE ceased being a non profit. Grasso argued that his pay was legal because the NYSE board -- comprised of some of the most prominent CEOs on Wall Street and corporate America -- unanimously approved his yearly salary and retirement package.

Despite his public neutrality, Grasso is believed to be in favor of spurning the Nasdaq and offer his approval of the Deutsche Boerse bid out of allegiance to the institution he worked at for more than 30 years and built into one of the world's most recognizable brands before his forced departure. His support would likely carry weight with many shareholders and NYSE market participants, who continue to hold Grasso in high regard and feel he has been unfairly treated since his ouster.

Charles Gasparino joined FOX Business Network (FBN) in February 2010 as Senior Correspondent.