JOHN SMITH'S GRAND NATIONAL Aintree, Saturday 9 April, 1615 BST
Live on BBC TV, HD, Radio 5 live, online
Other races also across the BBC 7-9 April
In Walsh's absence, Nina Carberry is the only female jockey in the race
Our Monty has pulled out of Saturday's Grand National with a leg infection.
The eight-year-old was to be ridden by Katie Walsh, sister of two-time winner Ruby, in her Grand National debut.
"He has picked up an infection in his front leg. It won't clear up before the weekend," trainer Willie Mullins told the Racing Post.
The withdrawal guarantees the Howard Johnson-trained Royal Rosa a run as he is comes into the field from number 41 on the list.
Skippers Brig is the next in line to be promoted in case of another non-runner.
The best-fancied of Mullins' three remaining hopes is gelding The Midnight Club, piloted by Ruby Walsh, who is set to start amongst the favourites.
Dooneys Gate and Arbor Supreme will also represent the Irishman.