的幸运日

someone’s lucky day

→ 的
phrase Rare #25,891
someone’s lucky day 的 marks possession and follows the person or pronoun whose lucky day it is.
CH: 今天真是我的幸运日。
EN: Today really is my lucky day.

真是我的幸运日

This is really my lucky day.

— 虎胆龙威 (1988)

一定是你的幸运日

It must be your lucky day.

— 虎胆龙威 (1988)

他说今天是他的幸运日

He said today was his lucky day.

— 调音师 (2018)

今天是我的幸运日

Today is my lucky day.

— 第五元素 (1997)