Humpf. I'm torn between these two words. They're both adverbs, but the "humbly" is the one I wrote first, though it looked wrong to me. Then I looked it up. It was spelled correctly. But then I came across "humblingly," which is what came across my mind at first, but the three syllables seems a bit much.

What do you think? Which word is more appealing to you.

... humbly/humblingly admit.