Undoubtedly is an adverb meaning “without doubt” or “certainly.” It’s a somewhat less formal alternative to “ indubitably .” It can be used at the beginning, middle, or end of a sentence to express a viewpoint or evaluation.

very likely; almost certainly: It is undoubtedly one of the best movies of the year. The highlight of the evening was undoubtedly (= without a doubt) the speech by the guest of honor. (Definition of undoubtedly from the Cambridge Academic Content Dictionary © Cambridge University Press)