Though he has yet to publicly address the news, according to a source, Rob, 31, is “furious” at Thompson, 27, for allegedly cheating on his sister Khloé Kardashian, 33, throughout her pregnancy.
“Khloé has always been there for Rob and he hates that she was hurt — he knows what it feels like to be screwed over by someone you trusted,” says the source of Rob, who has an infamously rocky history with his ex, Blac Chyna.
Adds the source: “Rob won’t forgive Tristan for this.”
Khloé and Thompson welcomed their first child together, a baby girl named True Thompson, on Thursday — just days after allegations surfaced that the Cleveland Cavaliers player had been unfaithful to the reality star multiple times.
RELATED: Everything We Know About Tristan Thompson’s Cheating Scandal
And Rob’s not the only member of the famous family outraged by the news: On Tuesday, a source told PEOPLE that Kim Kardashian West, 37, and her husband Kanye West,…