The Oscar-winning screenwriter was accompanied to a special BritWeek luncheon at the Four Seasons hotel in Beverly Hills by actress Michelle Dockery, who plays Lady Mary Crawley in his hit period drama.
BritWeek, founded by TV guru Nigel Lythgoe, is held annually to recognise the relationship between the U.K. and Hollywood, where Fellowes said he has been overwhelmed by support for Downton Abbey.
Fellowes says, "California is a wonderful, tolerant and encouraging host for ideas and for people of every denomination, and it is no surprise to me that we should find such a marvellous celebration of the achievements of the British under its azure skies. I am proud to be part of this year's BritWeek...
"The American response to the show has been extraordinary and really one of the nicest parts of the whole adventure."
The 7th annual BritWeek will be held from 23 April to 6 May (13), and will feature a charity ball, music festival and business awards.