Hilary Duff celebrated National Siblings Day by sharing her love for sister Haylie Duff, while Erika Christensen chose to embrace her onscreen siblings instead.

#NationalSiblingsDay

Friday, April 10, was National Siblings Day, a not-yet-official holiday where siblings are encouraged to celebrate each other. Most choose to celebrate by sharing a fun photo on Twitter or Instagram, and a lot of celebrities joined in on the fun.

Hilary Duff shared a montage of pics on her Instagram page for her sister Haylie, writing, “I love you more than words.”

@haylieduff I love you more than words #nationalsiblingday

A video posted by Hilary Duff (@hilaryduff) on Apr 10, 2015 at 11:08am PDT

Erika Christensen took advantage of the holiday to celebrate her fictional siblings from the NBC drama Parenthood.

Is it really #NationalSiblingsDay? Because… pic.twitter.com/ZuiF9wn1R3

— Erika Christensen (@ERIKAjaneC) April 10, 2015

Fellow Parenthood actress Mae Whitman also celebrated her onscreen family, sharing a photo of her fictional brother, Miles Heizer.

happy siblings day, love of my life @younggoth

A photo posted by @mistergarf on Apr 10, 2015 at 1:58pm PDT

Famous Disney star and twin, Cole Sprouse celebrated on Twitter with a heartfelt message for his brother, Dylan: “I was the original cell.”

.@dylansprouse I was the original cell. #NationalSiblingsDay

— Cole C. Sprouse (@colesprouse) April 10, 2015

Celebs Share Throwback Photos For #NationalSiblingsDay

Other celebs shared some throwback photos, like Lucy Hale, Rumer Willis, Ryan Phillippe and Mario Lopez.

Happy National siblings day Magssss. Thanks for putting up with my crazy ass since forever.

A photo posted by Lucy Hale (@lucyhale) on Apr 10, 2015 at 10:29am PDT

Happy National Siblings Day to these two baes @buuski #freeslw and our two little munchkins #mabel&evelyn

A photo posted by Rumer Willis (@ruelarue) on Apr 10, 2015 at 11:54am PDT

Every day is national sibling day.

— Scout LaRue Willis (@Scout_Willis) April 10, 2015

My sisters and I…. Sandy and Tracey #nationalsiblingsday #flashbackfriday pic.twitter.com/5G4QsJYaZc

— Tim McGraw (@TheTimMcGraw) April 10, 2015

me n my lovely sisses thx mom n dad for putting us all together. @katelyn_phillippe @lindsay_foret @kirstenmucha #nationalsiblingsday

A photo posted by r.p. (@ryanphillippe) on Apr 10, 2015 at 11:09am PDT

Blessed with the best sister ever. Thank you for always having my back… Love you Marissa! #NationalSiblingsDay pic.twitter.com/V3xxkEyM4S

— Mario Lopez (@MarioLopezExtra) April 10, 2015