Hilarie Burton shares sweet message for Sophia Bush on her birthday: See cute photo

"One Tree Hill" star Hilarie Burton is celebrating her former co-star, Sophia Bush , on her birthday.

On Monday, Burton shared a heartfelt message to Bush on Instagram featuring photos of the two of them from when they were young kids, and also wrote about how their opposite upbringings eventually led to their friendship years later.

Burton, whose birthday was a week ago, began her message to Bush with, "Once upon a time, in the year of our Goddess -- 1982 -- two little girls were born in the same week, but on opposite sides of the world."

"These little nerds loved school and books and camp and extracurricular activities to pad their college resumes….and they were the same kind of animal," she continued. "Ambitious. Persistent. LOUD. Dramatic. But they were also a marriage of opposites. Dark and blonde. Petite and tall. California and Virginia. All girls school and public school. If there was ever a case of Nature vs Nurture, this was it."

"The older one looked mean and angular and tough. But was a wuss on the inside. Easily hurt," Burton added. "The younger one looked adorable on the outside. …And so it came to pass that the Universe, in all her infinite wisdom, threw these two together and created a perfect storm of sisterhood and feminine rage and salacious gossip and soft, loving trust. It was perfect. You, @sophiabush, are perfect."

Burton went on to say that while she feels "guilty that my birthday comes first," Bush always takes the time to "make me feel so loved."

She ended her message to Bush, her friend of more than two decades, by thanking her for "always seeing the deep down me, and protecting her."

"Thank you for all the generosity and silliness and partnership," she added. "Everything you touch ends up better. Shinier. Happier. We have so many good things planned for this year."

"Here's to more and more and more," Burton said.

For Burton's birthday last week, Bush also shared a sweet birthday tribute to her friend on Instagram , in which she called Burton her "sister."

"Same squeeze, all these years later," Bush said in her post. "Same love, just multitudes greater."

Bush and Burton both starred on "One Tree Hill" when the show premiered in 2003. Burton portrayed Peyton Sawyer while Bush played Brooke Davis.

Burton left the show after season six, while Bush starred in the show until its final season.

Since starring on the show together, Burton and Bush have remained close friends and continue to support each other.