The 38-year-old actor penned an adoring message to the actress on her birthday Wednesday following news Reed is pregnant with their first child.
"Happy Birthday to the most amazing human I know... Today, we celebrate you," Somerhalder captioned a series of photos from throughout their relationship. "It's your day.
"The love and light you radiate to the world shines like a beacon for all to see. It's that love and light that guides me to the safe shores of home from the turbulent and sometimes treacherous waters of life," he wrote.
"Thank you for your tireless pursuit of spreading good, being an instrument of change and seamlessly weaving the complex threads of our lives together into the warmest, softest and most magical blanket," the star added.
"Every day I get to watch you being you I'm constantly reminded of your beauty and prowess and how lucky I am to share this life with you."
Somerhalder and Reed married in April 2015 after less than a year of dating.
The actor confirmed May 4 that he and Reed are expecting by sharing a photo of himself kissing the actress' baby bump.
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"In my 38 years on this earth I've never experienced anything more powerful and beautiful than this," he said at the time. "I can't think of anything more exciting than this next chapter and we wanted you to hear this from us first."
Somerhalder is best known for playing Damon Salvatore on "The Vampire Diaries," which came to a close in March after eight seasons.
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