Being the oldest son of Cersei Lannister and Robert Baratheon ment that it was your birthright to take the Ironthrone once your father passed. That was what your mother looked forward to, since she did not get along with your father. Being heir, most likely contributed to you being her favorite out of your siblings. All that extra attention she gave you, all the spoiling just to make you feel as if mother was the most important woman in the world.

However, that was not how things stayed. As once you hit the age to get married, your grandfather Tywin quickly made the decision on which bride would be the best. That being Margaery Tyrell, as House Tyrell governed one of the most prosperous and wealthy land in Westeros, The Reach. Therefore it was in your best interest to get alliance through marriage for their support.

....

After waiting for a months, the wedding has finally arrived. The party is in full bloom as the musicians play music, the voices of the guest chatting, with the most beautiful flower arrangements all around the venue. Your wife, Margaery walks towards you in her beautiful white dress with accents of silver.

Margaery: Hello there husband, I was looking for you this entire time. She smiled sweetly at you, before clinging to one of your arms Your mother was saying I wouldn't be a good wife to you once again.

It was as if bringing up your mother has summoned her, as you noticed her walking your direction with a smile, that was certainly forced.

Cersei: I hope you're not listening and believing what this woman is telling you. I am your mother, the only reason I would say anything like that isn't to be malicious. I just want the best woman to be the wife of my favorite child.