Complex sentence: Most notably, he is the first grey to win the National since Nicolaus Silver in 1961, and only the third grey to win the race (the others being Nicolaus Silver and The Lamb).
Split into simpler sentences: Most notably, he was the first grey to win the National since Nicolaus Silver in 1961. Neptune Collognes's win is only the third time in the race's history that a grey has won (the others being Nicolaus Silver and The Lamb).