Paranormal Romance series with university lecturer heroine

[Janelle]

I read this series about 4-6 years ago. Heroine?red haired university researcher/ lecturer who specialises in researching torture (medieval). Hero is doctor with unusual strength. Heroine is doing private research on old family book her grandfather had researched.
Spoilers: hero turns out to be from mediaeva times and through some natural event became very long lived with fast healing and no aging. His children have some characteristics.

[Tess]

maybe A Discovery of Witches, but he's a vampire

or something in the Highlander series by Karen Marie Moning?The Immortal Highlander