Which is really quite daft - because it was Senesino, not Farinelli, who had the feud with Handel. 

The first the general public knew of the feud was a letter that appeared in "The Bee", 2nd June 1733:


We are credibly informed that one Day last Week Mr H-l, Director-General of the Opera House, sent a message to Signior Senesino, the famous Italian Singer, acquainting Him, that He had no further service of Him; and that the next day Senesino replied by a letter, containing a full Resignation of all his Parts in the Opera.....
... the World seems greatly ASTONISH'D at so unexpected an event; and that all true lovers of Musick GRIEVE to see so fine a singer dismissed in so critical a Conjecture.


Partisan musicography of the Proutian kind for years conjectured that Handel had caught-out Senesino in the plot to establish a rival opera company - revealed in a letter of "Jan 13th, 1733" (from Baron De La Warr to the Duke of Richmond).  This all showed that poor old Handel had been conspired against by a despicable team of foreign eunuchs.  However, the letter was wrongly dated - in fact, it's from JUNE 13th - the week AFTER Senesino was fired.

Things now look entirely different.  Handel evidently fired Senesino for some other reason, of which we aren't aware now.  But whatever that reason was,  it now seems that Senesino began to gather his creative team and financial backers for the "Opera Of The Nobility" (which wasn't ever really called that, but it's a handy term) - in revenge for what we would these days call Unfair Dismissal.   Of course, it was later seen as a "Handel Vs Bononcini" shoot-out, but in reality the prime mover and shaker was Senesino - knowing very well that it was the singers whom the public came to hear, not the composers.  However, Senesino needed the "credibility" of a Music Director with credentials, and Bononcini was more than happy to join Senesino's cause - as were almost all the other singers, on the promise of better pay and conditions, and no dictatorial Handel in charge. Happiest of all would have been the librettist, Rolli.  He'd had to suffer the indignity of being sidelined by Handel in favour of librettos written by someone with no literary qualifications at all - the cellist Nicola Haym, who stage-directed his own pieces with aplomb in triumphs like GIULIO CESARE.  Rolli, by comparison, had no experience in the theatre at all, and relied upon his fine versification..  which presumably went over the heads of the anglophone audience.  But in the new scheme of things, Rolli was not only made librettist for a financially flourishing outfit, but was made titular academic "head" of it too.  (Sadly for Handel, poor Haym died in the interim, leaving him without a librettist at all).

The "opera wars" that followed are now legendary - but as far as we can now see,  Handel seems to have provoked them himself, by inexplicably and extemporarily firing his notoriously temperamental lead performer in a public and humiliating way.

Farinelli was later brought into the Senesino company, by Senesino himself - and the two men appeared in the same casts.  To Handel's anger no doubt,  Senesino decided to repeat his triumph in OTTONE - one of Handel's works.  Farinelli was given the role of Adalberto (previously by the German castrato Berenstadt, under Handel's direction).  Handel, however, was not invited to participate at all.  Legend has it that he bought himself a ticket in the middle of the Stalls, and sat there huffing and puffing throughout the performance of his opera under Bononcini's direction