Sarek Cast in Star Trek: Discovery

A new member of the Star Trek: Discovery cast has been announced. James Frain (The Tudors, Gotham) has joined the cast as Sarek, the father of Spock. Since the series only takes place 10 years before the Original Series then Spock would have been a recent new member on the USS Enterprise under Christopher Pike. Sarek's pre-TOS duties are unknown but likely he was part of the Vulcan embassy team to Earth so I imagine his role would be to represent Federation and Vulcan interests in whatever the main plot of the first season is. At this point it seems the question isn't if Spock's mother, Amanda Grayson, is part of the series but really what actress they will cast in the role.