(CNN) -- Red Cross President and CEO Mark W. Everson has stepped down after revelations he was "engaged in a personal relationship with a subordinate employee," the organization announced Tuesday.

Mark W. Everson says he is leaving his post, effective immediately, for "personal and family reasons."

The Red Cross Board of Governors asked for and received Everson's resignation after it "concluded that the situation reflected poor judgment on Mr. Everson's part and diminished his ability to lead the organization in the future," the Red Cross said in a statement on its Web site.

Everson, 53, said in a written statement that he was leaving the $500,000-per-year job "for personal and family reasons, and deeply regret it is impossible for me to continue in a job so recently undertaken."

Everson -- who is married and has two children -- joined the Red Cross as president and CEO last May.

The organization became aware of Everson's relationship with a female Red Cross employee 10 days ago, Chief Public Affairs Officer Suzy C. DeFrancis told CNN in a telephone interview.

"I think the board acted very quickly," she said, adding that the woman remains in her job.

About Everson, DeFrancis said, "We're grateful for his service."

The board of governors on Tuesday appointed Mary S. Elcano, general counsel and five-year Red Cross employee, as interim president and CEO.

Everson had worked in the Bush administration from August 2001 -- including serving as commissioner of the Internal Revenue Service -- until he was hired by the Red Cross.

"This is flabbergasting, that's all I can say. It's completely contrary to his public persona that he evidenced while he was at the IRS," said Suzanne Ross McDowell, a Washington-based attorney who served on an advisory committee to the IRS division that deals with tax-exempt organizations.

"From the standpoint of exempt organizations on the non-profit sector, it's just another news story that we would rather not see," she said.

"It's got nothing to do with the Red Cross," said Ira Milstein, a New York lawyer specializing in corporate governance who has worked with the organization and was impressed with Everson. "He was a team player and a good leader. To have him fall off a cliff like this is just sad."

A search committee has been formed to begin the process of finding Everson's permanent replacement, the organization said.

The job has been a challenging one. Marsha J. Evans resigned as president in 2005, after the Red Cross response to Hurricane Katrina came under fire.

Four years earlier, Bernadine Healy quit the post after the organization was criticized for mishandling donations intended for victims of the September 11 terrorist attacks and collecting vast quantities of blood that was not needed and ultimately thrown out.

Healy told reporters she "had no choice" about her resignation.

Meanwhile, DeFrancis acknowledged Tuesday that, 14 years after a court ordered the agency to improve its collection of blood, it has yet to meet federal safety and quality-control requirements. E-mail to a friend

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