You mean his half-brother Bertram, he first appears in Emission Impossible and returns in Sibling Rivalry, his final appearance (aside from him being the final boss in the Family Guy Video Game) is The Big Bang Theory.
He also makes a return appearance in the video game, Back to the Multiverse.
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In 'Stewie Griffin The Untold Story' Brian is seen paying bills for "this girl's house".
We can assume this girl was Jillian because when we first see her in 'Whistle While Your Wife Works', we find out she and Brian have been dating for awhile but the answer to your question is actually...
There is no episode where we see Brian meeting Jillian.
Dylan Flannigan. Brian discovers he has a son in the episode 'The Former Life of Brian' (UK season 8/US season 6)
Brian Does Hollywood
Brian the Bachelor (Season 4)
Brian: Portrait of a Dog
Saving Private Brian
Play It Again, Brian