It was all but certain even before Samsung launched the Galaxy S4, but now it appears to be official: the Galaxy S4 is Samsung’s fastest-selling smartphone ever. Korea-based  paper The Chosun Ilbo on Wednesday quoted an unnamed Samsung executive who shed some light on the blistering pace of Samsung’s S4 channel sales. In just five days following the smartphone’s launch, Samsung apparently sold 4 million units into channels. For comparison, the first Galaxy S line took 85 days for shipments to reach 4 million handsets, the Galaxy S II took 55 days and the Galaxy S III took 21 days. Through May 10th, two weeks after the Galaxy S4 began shipping, the anonymous executive said channel sales reached 6 million units. He also believes Samsung is on track to sell 10 million Galaxy S4 phones into channels by the end of May, which would be on par with analysts’ expectations.