Keith Olbermann abruptly bid farewell to his audience on Friday night, announcing that this would be the last edition of “Countdown,” the program he has anchored for eight years.

Keith_olbermann_058 The at-times controversial, always confrontational liberal host gave no explanation for his departure, but the timing — so soon after Comcast received approval of its merger with NBC Universal — is sure to raise eyebrows.

Beyond his own outspoken role, Olbermann’s program provided the launching pad for MSNBC’s two other primetime hosts: Rachel Maddow (who was conspicuously on vacation Friday, and very close to Olbermann) and Lawrence O’Donnell.

The website mediabistro.com/tvnewser has the following no-details statement from MSNBC:

MSNBC and Keith Olbermann have ended their contract. The last broadcast of “Countdown with Keith Olbermann” will be this evening. MSNBC thanks Keith for his integral role in MSNBC’s success and we wish him well in his future endeavors.

Last May, Comcast CEO Brian Roberts was asked about whether he was ready for the headaches associated with running NBC U during an interview at the Cable Show. Former News Corp. COO Peter Chernin specifically wondered what Comcast would do if an MSNBC host created a stir that threatened the company’s larger interests.

Roberts sidestepped the question, but did say regarding NBC News, “The single most awesome asset that comes from this deal is NBC News. … NBC News will help define Comcast.”

Olbermann served a brief suspension in November for unauthorized political donations, but he has been so closely allied to MSNBC Prez Phil Griffin that his exit has to come as a major shock. He’s also the latest high-profile talent or exec to leave since Comcast began taking over, including NBC U CEO Jeff Zucker, and entertainment execs Jeff Gaspin and Angela Bromstad.

Interestingly, Olbermann’s chief rival at Fox News Channel, Bill O’Reilly — who had frequently lashed out at General Electric because the company employed Olbermann — had speculated on the air that there would be changes at MSNBC once Comcast took over. That most likely was just bluster, though, not insider knowledge.

UPDATE: Was MSNBC prepared for the change? Apparently not. Thirty minutes after Olbermann announced he was leaving, the channel ran a promo for its “Lean Forward” campaign featuring — you guessed it — Olbermann.

 Also, Anderson Cooper is covering the story on CNN, with former MSNBC anchor David Shuster among those commenting. (Be interesting to see if Fox News does any gloating next week.)

“He’s resurfaced before, he’ll resurface again,” Shuster concluded.

 Second Update: Both Comcast and MSNBC have denied that the new owner played any role in the decision. Given that Comcast had already put its management team in place before receiving FCC approval, I find it hard to believe that any major personnel decision would be made without at least a heads up to top brass.

Certainly, those looking for conspiracies won’t find the channel backing off its liberal niche with its new lineup of O’Donnell, Maddow and Ed Schultz in primetime.

Nevertheless, Olbermann not only helped define the network but steered the channel into its current profile. As is so often true in TV, form follows success, not the other way around.