The king said: 'Do not be offended with us, neither you nor your forefathers, because this knowledge has before now never dwelt with any Brahmana. But I shall tell it to you, for who could refuse you when you speak thus?

In plain words: The king asks Gautama not to be offended, explaining that this knowledge had never before belonged to any Brahmin priest. Still, he agrees to teach him because Gautama asked so sincerely.