The 50-year-old English actress discussed her relationship with the 55-year-old actor on Wednesday's episode of Lorraine. Hurley and Grant were together for 13 years before splitting in 2000, but remained close after their breakup.
"He's still my best friend and he's very important to me," the star said before calling Grant family. "I think families change. I think they used to be much more insular but now friends become as important as some family members sometimes."
Hurley previously told Watch What Happens Live she and Grant split in part because of the actor's grouchy personality. She told host Andy Cohen she finds the actor's grumpiness "very charming" but isn't able to deal with the trait 24/7.
"He remains my best friend to this day, but -- I mean, I'd say this if he were here sitting here -- he used to really annoy me," she admitted. "I mean, I love him, but he's very annoying. He is [very cranky and curmudgeonly]. My friends used to call him 'grumplestiltksin.'"
Grouchiness aside, Hurley named Grant godfather to her son by Steve Bing, Damian Charles Hurley, who is now 13 years old.
Grant himself is father to four children, including an infant daughter born to Anna Eberstein in December.
Hurley plays Queen Helena on E! series The Royals, which was renewed for a third season in January. Grant last appeared in The Man from U.N.C.L.E., and will next star in Florence Foster Jenkins with Meryl Streep.