Dear [Friend's Name],

I hope this letter finds you well. I wanted to apologize for missing your birthday party. I was really looking forward to celebrating with you, but unfortunately, something unexpected came up at the last minute and I couldn't make it. I hope you understand and forgive me for not being there.

I'm sure the party was amazing and filled with lots of fun and laughter. I would love to hear all about it from you. Please tell me all the highlights and special moments so that I can feel like I was there in spirit.

I still have your birthday present with me and I would love to meet up with you soon to give it to you in person. Let's plan a get-together over coffee or lunch so that we can catch up properly. I really value our friendship and I don't want to miss out on any more special moments with you.

Once again, I'm sorry for missing your party and I hope we can make up for it by spending some quality time together soon.

Looking forward to hearing from you.

Warm regards,
[Your Name]