Thank You For Thank You to Mentor
Dear {Mentor},
The progress I've made in my career over the past {number of} {months/years} has been incredible, and I owe it all to you.
You've taught me so much, and your {guidance/training} in {topic} has led me to {achievement}. Before working with you, I struggled to {describe difficulty}. Now, I {elaborate on achievement}.
I've also noticed a big change in {area}. I no longer {describe difficulty}. In fact, I {elaborate on achievement}.
Thank you for believing in me and for always pushing me to challenge myself. I am grateful to have you as my mentor and my friend.
{Your Name}