He is the creator of Downton Abbey, used to being feted by Hollywood's A-list, with leading stars pleading for a role in the hit drama.
But Lord Fellowes has been left in shock by the emergence of a secret email written by a Hollywood mogul damning him as 'awful' - and snubbing the Oscar winner for another writer.
The insult to the Tory peer - written by his own former agent - is among a series of bombshell emails leaked on to the internet revealing the inner workings of Hollywood.
Lord Fellowes, 65, last night described the comments by Brian Siberell - one of the film industry's most powerful men - as 'disappointing and surprising'.
Siberell's comments are among more than 40,000 leaked emails and documents hacked from Sony studios and published by the WikiLeaks website last week. The documents, which have sent shockwaves through Hollywood, also reveal that:
• The producers of the new Bond film Spectre considered casting Meryl Streep as a female Blofeld, the coveted 'baddie' role played by Donald Pleasence in 1967 in You Only Live Twice.
• 12 Years A Slave actor Chiwetel Ejiofor wanted the pivotal Blofeld role in the new film.
• David Cameron's advisors dropped plans to invite A-list stars like Brad Pitt and Angelina Jolie to a Downing Street reception, worried 'vicious' newspapers would accuse him of courting favour with luvvies.
Siberell, a leading player at the Creative Artists Agency, trashed Fellowes in an email exchange with Sony executive Amy Pascal when they discussed plans to remake the 1968 Oscar winning musical Oliver!
The pair were judging the merits of possible writers for the film, including Fellowes and fellow Oscar-winner Christopher Hampton, who wrote Dangerous Liaisons and the Andrew Lloyd Webber musical Stephen Ward.
On April 10 last year, Siberell wrote: 'Of the writers whom you named there is the awful Julian Fellowes. Christopher Hampton I like of course, though his recent show with Lloyd Webber stumbled.'
A stunned Lord Fellowes, who was represented by CAA in the late 1990s, last night said: 'It's quite disappointing but on the other hand, I left CAA because nothing was happening for me and now I understand why.
'Having an agent is like any other key relationship in your life. If it works well its the absolute magic carpet but you have to be aware of the fact that there is an element of luck. Sometimes it just doesn't click.
'I don't think I am a bad writer. I don't think Brian is a bad agent. We didn't click, so I moved on to Independent Talent where I have been very fortunate.'
Lord Fellowes, who along with his Oscar for Gosford Park now also boasts a Golden Globe and an Emmy, said he was fully aware that not everyone was in awe of his work. He said: 'For everyone who admires me, 20 wish me at the bottom of the sea. You have to carry that in the load to be honest.'
He added that there was no point bearing grudges about such things. 'He has no particular reason to love me and is entitled to say what he wants,' he said.
It is believed the newly disclosed emails were among many thousands of documents hacked from Sony last year, possibly by the North Korean government. The documents have only now become available on the internet in their entirety.
In one email, Sony executive Jonathan Glickman tells a colleague: 'Blofeld as a woman is idiotic unless Meryl Streep does it.'
The role is rumoured to have gone to Christoph Waltz. In another exchange, Bond producer Barbara Broccoli reveals Oscar-nominated Chiwetel Ejiofor talked to director Sam Mendes about the coveted baddie role. 'Sam spoke to Chiwetel who wants to play Blofeld,' she wrote.
Chiwetel Ejiofor. Photo / Getty Images
The emails also reveal that Culture Minister Ed Vaizey wrote to Sony chief executive Michael Lynton last year seeking advice on who to invite to a star-studded 'creative industry' Downing Street reception.
But it appears No 10 officials feared negative comparisons to Tony Blair's 1997 'Cool Britannia' bash.
In the event, a largely British contingent of stars attended.
A source at Sony said: 'The latest move by WikiLeaks to put all this information out there has sent a shudder through the ranks.'
Mr Siberell last night told the Mail on Sunday: 'I don't remember writing it, but suspect I was just feeling prickly as Julian is so maddeningly gifted. The fact remains I love him.'
