Kim Kardashian has wished her father a happy birthday on what would be the start of his 73rd year. In doing so, she’s made public a beautiful family tradition.

The reality TV star shared an old family photo on Twitter.

Happy Birthday dad! I love this family photo. I love our family. Thank you for EVERYTHING. I’m so grateful you are my dad! pic.twitter.com/0AAyqCu0nM

— Kim Kardashian West (@KimKardashian) February 22, 2017

She said she found a letter her dad wrote her just after high school. Kim, now 36, was 23 when he passed away.

“I found a three page letter my dad wrote me right after high school about life and it’s so special to have. I re-read it last night,” she posted to Twitter.

The letter has started a tradition for Kim, who writes to her kids – North West, 3, and Saint West, 1 – every year. She wrote on Twitter:

I write my kids a letter each year reflecting on the year we had together & fun memories. I’ll give the letters to them when they turn 21 ❤️

— Kim Kardashian West (@KimKardashian) February 22, 2017

It’s a touching sentiment, and one that gives us a very personal look into the life of a family we spend a lot of time watching, and very little time trying to understand.