The Virgin - S4-E10
Elaine: Look at George. He lucked out, huh?
Jerry: Oh, you're not kidding. Who'd have figured Susan would break up with him? They had a good thing going.
Elaine: Yeah. Since she met him, she's been vomited on, her family's cabin's been burned down, she learned her father's a homosexual, and she got fired from a high-paying network job. Yeah, they had a real good thing going.
Chosen answer: George does mention his brother in the episode "The Parking Space". They actually really never mention anything that contradicts the fact he had a brother though, it just isn't mentioned.