Joseph O'Brien's string will be split 50-50 between Flat horses and jumpers when he starts training full time.

O'Brien, twice champion Flat jockey in Ireland, has quit the saddle to concentrate on his new career.

The 22-year-old has been playing a key role in helping his father, champion trainer Aidan O'Brien, with a large string of horses, including Triumph Hurdle favourite Ivanovich Gorbatov, from a base at Piltown, County Kilkenny.

"My grandad trained from here and both my mum and dad trained from here. The last couple of years we'd had horses back here and it's gone on from there," O'Brien said.

"I'll just take things as they come and do my best with every horse that comes in and go from there.

"Hopefully I'll have the licence for May.

"We're pretty much 50-50 jumpers and Flat horses. We've got a nice bunch of two-year-olds and some National Hunt horses.

"Hopefully we can get a few winners when the season gets going."

Tall for a Flat jockey, O'Brien was always likely to find his battle with the scales proving too much.

"Starting off, I never thought I would be able to ride for an awful long time," he said.

"I was very lucky to ride some very good horses. I was in the right place at the right time."

Of his many big-race triumphs, O'Brien rates the Epsom Derby, which he won twice on Camelot (2012) and Australia (2014), and the Breeders' Cup Turf on St Nicholas Abbey in 2011 as career highlights.

"Riding the winner of the Derby is something else. It's the history the race has and everything about it," he said.

"The Breeders' Cup is a huge stage and to ride there was unbelievable and to win there was something you wouldn't even dream about happening.