Ken Boessenkool, a former adviser to Prime Minister Stephen Harper who was appointed to the B.C. job in January, met with the premier over the weekend and resigned with a letter of apology.
The letter, released by Clark's office on Monday, shed little light on the reasons for his departure.
"Earlier this month, I was involved in an incident where I acted inappropriately," Boessenkool wrote in his letter, dated Sunday.
"I was wrong, regretted my behaviour very much and immediately and unconditionally apologized. ... This (my resignation) will give me a chance to return to Calgary to be with my family — who I have also let down — and from whom I have been separated on a weekly basis for most of the last eight months."
Beyond that, Clark declined to provide many details, citing privacy laws.
The premier said she learned about the incident about two weeks ago and the allegations were then investigated. She said there are no allegations of criminal conduct.
She met with Boessenkool on Sunday.
"It was a quick investigation and I made my decision immediately after the investigation was done," said Clark.
"He and I agreed that he should resign. I certainly, when I sat down with Ken, I knew that he had to resign, and he agreed that that was the right course to take."
Boessenkool, who once described himself as coming from "the womb right wing," was appointed to the premier's office in January at the same time Clark appointed a former Harper communications staffer as her press secretary.
Boessenkool's resume includes time as an adviser to Harper, a Tory election strategist and a lobbyist for companies such as Enbridge Inc., Taser International and several pharmaceutical firms.
In 2001, Boessenkool signed the notorious "firewall" letter that urged Alberta to fight Jean Chretien's Liberal government. The letter, also signed by Harper, who was then president of the National Citizens' Coalition, urged Alberta to build firewalls to limit what it argued were federal intrusions into the province.
Longtime bureaucrat Dan Doyle is taking over as Clark's chief of staff — an appointment the premier attempted to use to wipe off some of the stain left by Boessenkool's mysterious departure.
Doyle, a recipient of the Order of B.C., had a long career working in government, including a four-year stint as a deputy minister. He worked with the organizing committee for the 2010 Winter Olympics in Vancouver and had been working as chairman of the B.C. Hydro board.
"He is the guy who can step in and make sure we don't miss a beat," said Clark.
"That cabinet room is pretty familiar to Dan Doyle. We're not missing a beat."
Clark's Liberals have been slumping in the polls and losing a number of high-profile members of cabinet and caucus ahead of next May's provincial election.
But the premier rejected the suggestion that Boessenkool will further damage her party and her re-election prospects.
"I focus on what's happening next and how we can stay focused on growing jobs and growing the economy," she said.
"That's why Dan Doyle chose to take on this job. It's not an easy job."
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