When the show was first being cast, the role of Darrin was originally offered to Dick Sargent. He had to turn it down due to other contractual obligations, with the part then going to Dick York. When York could no longer continue on the show as a result of declining health, Dick Sargent was once again offered the role, and this time, was able to accept.
Your screen name reminds me of another actor who recently passed away this year - Van Williams, who played the Green Hornet.