4x23/24 "The One with Ross's Wedding"

All the friends go to London, except for Phoebe, who's pregnant and Rachel, who thinks it will be too painful to see Ross get married, and tells Ross she has to work. The building where Ross and Emily schedule to get married has been torn down a few days early, but they decide to marry there anyway. Richard Branson cameos as a souvenir stand salesman, and Sarah, Duchess of York, appears in a video with Joey. Rachel decides to go to Ross's wedding after all, to say she still loves him. Emily's parents try to fool Ross's parents with the wedding bill, paying to remodel their house as well. Chandler and Monica sleep together after a drunk guy thinks she is Ross's mother. At the altar while Ross is saying his nuptials, he makes a big mistake and says Rachel's name instead of Emily's.