Step-brother Turns My Engagement Dinner into a Gender Reveal, so I Send Him the Bill. AITA?

Family dynamics can be complicated, especially when step-siblings are involved. In this case, the OP's stepbrother Ethan has a history of being competitive and attention-seeking. However, he seemed to have matured over the years and even asked the OP to be an aunt to his future child. But at the OP's engagement dinner, Ethan and his wife showed up uninvited and turned the event into a gender reveal party for their own baby. This understandably upset the OP and her fiancé, who had paid for the expensive dinner. In an attempt to do some damage control, the OP sent Ethan the bill for half of the cost. However, Ethan was not happy about this and argued that he didn't intend to hijack the event. The situation escalated into a fight, with the stepmom getting involved and suggesting that the OP's fiancé could just have a second engagement dinner. But the OP is standing her ground and demanding that Ethan pays. What do you think? Should Ethan be responsible for paying for his unexpected and unsolicited announcement? Share your thoughts in the comments below.