After a very unexpected talk between Celestia and Twilight, Luna returned to Celestia's sleeping chambers and almost immediately Celestia began to lick her chops over what she smelled, a freshly baked cake. Luna levitated the cake to her sister, hoping that it would be the best she ever ate. As Celestia held the cake in front of her, it was all she could do to not just dive in and begin gorging herself on it but she had told Twilight that she was going to tell Luna that regardless, she would not have to pay up.
She sat the cake down on her bed which brought out concern from Luna, "Sister, what is it. Why aren't you diving in on your cake like you always do?"
Celestia replied, "I am not doing so because I need to tell you something."
Luna asked, "What is it sister?"
Celestia replied, "Twilight and I had a long talk while you were gone and a lot of things she told me and questioned me about this whole situation made me do some deep thinking."
Luna asked, "Oh?" She then turned to Twilight and asked, "What is it you talked to her about?"
Twilight replied, "We talked about this whole situation, we talked about what she wanted you to do and given that you two made this bet when you were fillies, I brought up all the silly bets that my brother and I would make when we were growing up. I also brought up how that no matter what, the loser never had to 'pay up.'"
Celestia added, "That was one thing that made me realize that this whole thing is wrong. Also, Twilight helped me realize that taking you two away from one another and forcing you into do something that would amount to cheating was wrong as well."
Luna gasped, "Seriously?"
Celestia replied, "Yes, seriously."
She turned to Twilight and motioned for her to continue, "Luna, I love you and I was not about to let Celestia take you away from me, even if it was just for a month whether it be simply being her chef or doing things I'd rather not think about."
Celestia added, "She helped me realize that what I was going to do was not only selfish, but very disrespectful so I have decided that whether this cake is the best or not, the bet is off. You will not have to pay up."
Luna was elated and Twilight could tell it. She flew to Luna and they engaged in a tight embrace. Both broke down in tears of joy and seeing this caused Celestia to realize that they truly did love one another. Gone was the image of them having a heated make out session on Twilight's balcony, what she saw now was a truly loving couple that she couldn't tear apart.
Soon though, her thoughts would turn elsewhere, "I'm not sure about you two but I'm hungry. How about we go down to the dining hall and have some cake."
The two broke their embrace and in unison they asked, "Cake? You're going to share your cake with us?"
Celestia replied, "Of course!" She turned to Twilight and continued, "Twilight, you have helped me realize the error of my ways and I think it is worth celebrating with the two ponies I'm closest to."
Luna replied, "That sounds good to me, what about you Twilight?"
Twilight added, "It sounds good to me too."
The three headed down to the dining hall and much to both their surprise, Celestia grabbed plates and forks for all of them. As she cut the cake and gave them their share, she gave the two a smile and said, "I give you two my blessing, may your relationship be eternal and filled full of happiness and love."
In unison the two replied, "Thank you for your blessing."
Celestia then turned her attention to her cake and said, "Now let's eat while this is still somewhat warm. Cake is always the best while it is still warm!"
What seemed to be a bad situation where Luna would be stuck doing something that she had absolutely no desire to take part in wound up being a truly wonderful day for not just her, but Twilight as well. At first both of them thought this would not happen but Celestia wound up giving them her blessing which is what they truly wanted.
For Celestia it was a day of change. That day, especially after a stern talking to from Twilight, she realized that old bets are just that, old. She also finally saw how much Luna and Twilight meant to one another and couldn't help but be happy for them.