walk in on somebody
From Longman Dictionary of Contemporary Englishwalk in on somebody phrasal verbINTERRUPTto go into a room and accidentally interrupt someone who is doing something private that they would not want you to see → walk→ See Verb tableExamples from the Corpuswalk in on • Ever walked in on a really deviant scene?• The Rector walked in on Freddie the lion and his sleeping mate.