Dear Mr.”Mentor’s Name”,
Initially, I didn’t really think that I would be writing a letter of gratitude for you because you seemed quite strict but in the times to come you proved to be the best person and someone who is so modest and down to earth.
This internship helped me apply all my theoretical concepts in practical life and it has literally opened the gates of new experiences for me where I wouldn’t just think of books but rather their application in real life. Your extensive experience have helped me and you have guided me as no one else would.
I am grateful for this opportunity and I would definitely want to collaborate in future again and learn many more things form you. No words world convey my gratitude to you for changing my perspective and hence do let me know if you would ever again need an assistant in the future.