While he was preparing Lennox's room three days before he arrived from abroad to discuss his recent collaboration with his father, Carlos overheard him talking to his two personal assistants about how he would present the project on his own without giving Lennox credit for his participation in it.
Carlos felt it was yet another betrayal. Richard had already destroyed Harvey's life, and now he was targeting his son for his personal gain. Carlos couldn't believe Richard would stoop so low and betray Lennox because the latter was clearly casting a dark shadow over his accomplishments. He never thought Richard viewed his son as a threat to his own success, but it became evident that Richard's ego and desire for recognition knew no bounds.
Carlos's hatred toward Richard ignited again, which was why he was easily convinced to betray Richard in the end.