Answer:
This is a catchphrase by Bruce Forsyth, who has been a British celebrity since hosting the variety show "Sunday Night at the London Palladium" in 1958. He went on to host numerous game shows, and most recently has hosted "Strictly Come Dancing," which is the original version of what is known internationally as "Dancing with the Stars." He is also known as a stage performer.
Forsyth's audiences are often encouraged to finish the line, as he proclaims, "Nice to see you, to see you..." followed by the audience shouting, "Nice!"