Season 7, Episode 11 - "Santa's Secret Stuff"
22 January, 2007
Rather than celebrating Christmas while Rory is in London over the holidays, Lorelai and Christopher decide to put their holidays on hold until she returns. Turning up unexpectedly at the inn, Luke asks Lorelai to write a character recommendation letter for his custody battle over April. Lorelai first struggles, but remembers how important Luke has always been in Rory's life and writes the letter. Rory decides she will write an apology letter to her friend Lucy, explaining why she and Marty kept their past friendship a secret (Source: TV.com).

