When he was at Oxford he had been well known for concealing under a slightly rowdy exterior the highest spirits of any of the undergraduates.  He was looked upon as the most fascinating of _farceurs_.  It seems that he had distinguished himself there less for writing Greek verse, though he was good at it, than for the wonderful variety of fireworks that he persistently used to let off under the dean's window.  It was this fancy of his that led, first, to his popularity, and afterwards to the unfortunate episode of his being sent down; soon after which he had married privately, chiefly in order to send his parents an announcement of his wedding in _The Morning Post_, as a surprise.  Some people had come in after dinner--for there was going to be a little _sauterie intime_, as Mrs Mitchell called it, speaking in an accent of her own, so appalling that, as Vincy observed, it made it sound quite improper.  Edith watched, intensely amused, as she saw that there were really one or two people present who, never having seen Mitchell before, naturally did not recognise him now, so that the disguise was considered a triumph.  There was something truly agreeable in the deference he was showing to a peculiarly yellow lady in red, adorned with ugly real lace, and beautiful false hair.  She was obviously delighted with the Russian prince. 
What caused the individual in Sentence 4 to be "sent down"?
Married Privately