It’s something E.L. James did this year with The Mister, a story she had actually concocted before she began writing the fanfiction that eventually became Fifty Shades of Grey. However, along with that book release, she reported she was “nervous” about moving on from Anastasia Steele and Christian Grey, noting,
Article source: https://www.cinemablend.com/news/2489322/el-james-says-its-hard-to-get-away-from-fifty-shades-of-grey-wants-to-tell-other-stories