Keane was welcomed by a jubilant crowd in Glasgow las night.
Keane said: “It’s absolutely unbelievable. This is the reason I wanted to come to Celtic.
“These fans are unbelievable. I’d like to say thank you very much to everyone for turning out.
“I know it’s late, so thanks very much. I really appreciate it.”
Keane added: “Over the years, I have been a Celtic fan. It’s been a mad few days but I’m here now and hoping to bring a lot ofsuccess in these short few months that I am here.”