On Wednesday, Tumblr announced in an apparent about-face that it would be allowing paid advertisement on the popular blogging platform. David Karp, Tumblr CEO and founder, made the announcement at Ad Age's Digital Conference today in New York.

As recently as April 12, Karp told Ad Age that advertising was "a complete last resort." In 2010, the CEO famously said, in an interview with the Los Angeles Times, that the company was "pretty opposed to advertising. It really turns our stomachs."

Yesterday, however, the 25-year-old CEO added that putting ads on Tumblr Radar would get an advertiser 120 million impressions per day and will be available as of May 2.

Rex Sorgatz, a New York-based tech consultant, who attended the conference, told BetaBeat that it was the "strangest closing keynote speech I’ve ever seen."

"[Karp] was scheduled to talk for a half hour, but I think the whole thing lasted 7 minutes," he continued. "He cited some growth numbers, mentioned how much he appreciates the creativity within the advertising community, and then broke the news that Tumblr would be opening up that spot to advertisers."

One of the strangest elements, Sorgatz said, was how Karp ended the presentation: "He flashed his email address on the screens, took no questions, and then zipped out the building."

According to Ad Age, Tumblr recently passed its 50 million blog mark, and secured a total of $125 million in funding as of September 2011. For now, the company’s only revenue model is taking a cut of sales of special blog themes, and letting users highlight posts for followers for $1 a pop.