Use the adverb doubtless to mean "absolutely" or "without question." You could tell your brother that he'll doubtless be thrilled about the birthday present you got for him.
You might rule out several neighborhoods when you're looking for a new apartment to rent, knowing they'll doubtless be too expensive for you. When she invites you to dinner, your friend might warn you about her dad's long stories, adding, "He'll doubtless tell you the one about his trip to Europe during college." Doubt is at the heart of doubtless, from the Latin dubitare, "to doubt, question, or hesitate."