Well, come on now guys... There is a lot of reading on this subject to be had (I've read over 50 on Everest alone)
Hillary was the lead climber of the pair, and when he said that "Tenzing belayed me up the last slope" it sounded pretty authentic, and consistent with how things went on that last day.
Hillary's official position was that they both made it together, because, being a pair, who made it first should be irrelevant. Unfortunately, the local press were so ecstatic about one of their own climbing the mountain, they ignored Hillary, and were convinced that Tenzing had done all the work and made the climb first. Tenzing even signed a document to that effect, which he later retracted.