From Longman Dictionary of Contemporary Englishburst in on/upon somebody/something phrasal verbINTERRUPTto interrupt someone or something by entering a room, in a way that embarrasses you or other people I’m sorry to burst in on you like this. → burst→ See Verb table
Examples from the Corpus
burst in on/upon • Her habit of jealously bursting in on Gustave when he was dining with friends was notorious.• Finally she burst in on him with a big kiss.• They burst in on the somewhat startled signalman who was puzzled by the dramatic appearance of the two familiar faces.• Actually, he burst in on us. 