For my new series, Thank You Notes, I teamed up with Olay to challenge a group of women to surprise their role models — the women who inspired them to face anything — with a thank you note.

In this episode: I’m a big tennis fan… you can spot me at the U.S. Open each year, cheering on some of my favorite athletes. But my favorite tennis player of all-time might just be the legendary Billie Jean King, founder of the Women’s Tennis Association(@WTA.) And I’m not alone: Sofia Kenin, who recently won the Australian Open, also admires King — and tells her just as much in an episode of my new series, Thank You Notes.

In the video, Sofia — who’s the youngest American woman to win a Grand Slam singles title since Serena Williams in 2002 — thanks King for paving the way for women in their sport. “Your achievements, your activism and your optimism,” she says, “have opened doors for all of us.”