The Crown : who is...

[FoxtrotOscarFoxtrotOscar]

...the young doctor who acts as a go-between between Di and Andrew Morton?

James colthurst

Is that the husband of the carraige driving friend of Prince Phillip ?

No. The carriage driving friend is married to one of the Mountbatten grandchildren. So a cousin of DoE

This was a friend of diana

James Gilbey