Reed, 26, and Somerhalder, 36, dated for six months before getting engaged, reported Us magazine.
"Can't tell you anything about it other than I love it more than anything in the world!" Reed said when asked about the ring.
She was earlier married to singer Paul McDonald before separating in 2014. Their divorce got finalised two months back.
Somerhalder previously dated his 'The Vampire Diaries' co-star Nina Dobrev for three years before splitting in 2013.