Argentinian horse Sixties Song will break new ground as the first South American horse to compete in Britain when he runs in the King George VI and Queen Elizabeth Stakes at Ascot.

The four-year-old, who has claimed top-level victories in Chile and his homeland, will be ridden by Gerald Mosse after Tom Queally opted to ride at Newmarket on Saturday.

Mosse's big-race victories include the 2010 Melbourne Cup on Americain.

"It looks a very competitive race but he is the top horse in Argentina," Mosse told Press Association Sport.

"I'm excited to ride in the King George, it's a great race to be a part of."

Nico Gaitan Dassie, assistant trainer to his father Alfredo, said it was a dream come true to have a runner in the prestigious race.

"This is tough, but a really nice challenge for all of us. It is the first time a South American-trained horse has run at Ascot and we are delighted to be here," Gaitan Dassie said.

"If you compared this to football it would be like a guy who plays in an average team in Argentina and goes straight to play in the final of the Champions League. This is like a dream coming true."

Sixties Song is an outsider and although he has never run right-handed in his eight starts, Gaitan Dassie does not believe it will be a problem.

"He has never run right-handed, but after coming back to Argentina from Chile and after we decided to come here we moved the horse from San Isidro to Palermo racecourse," he said.

"Palermo gives us the opportunity to train the horse right-handed early in the mornings.

"The horse is very professional and smart and has done pretty well training for this race."