Letter to your friend explaining to him/her why you could not attend his/her birthday party

Your Address},

{City} {Pin Code}.

{Date}.

My dear Meena,

        Let me express my sincere regrets for not attending your birthday party. I received your invitation and I was sure to attend the function; but circumstances did not favour me and I could not come to your place. 

        I was eager to see you and our friends at your place. But my grandmother had a sudden heart attack. Her pain was unbearable. We had to take her to the hospital. I had to be with her all the while. My mother had to look after my younger brother who is not well. So I could not attend your birthday party. 

        I hope, you will forgive me for not coming to your place. My grandmother is still in the hospital. All the family members are anxious about her. 

        Please convey my regards to your parents and love to your sister. 

Your loving friend, 

X Y Z