When between the years 1968 and 1971 did Fonteyn and Nureyev dance Swan Lake at the Royal Ballet in London?

I attended a performance of Swan Lake at Covent Garden sometime between those years but cannot remember the precise year - any help?

When between the years 1968 and 1971 did Fonteyn and Nureyev dance Swan Lake at the Royal Ballet in London?
the only thing i can find is 1966. i know it doesn't fit, but from videos that's the year it was.