Paddy Pilley stepped in at late notice to take the ride on rank outsider Diore Lia in Saturday's Investec Derby at Epsom, after fellow apprentice Gina Mangan was prohibited from riding in the premier Classic by the British Horseracing Authority due to her lack of experience.
Diore Lia's participation was placed in doubt, but it emerged on Thursday morning that she would indeed be declared with Pilley on board.
While Pilley still claims 5lb, his boss Roger Charlton and his jockey coach, Derby-winning rider John Reid, spoke highly of him when consulted by the BHA.
Pilley said: "I'm excited as it will be a big day out and it will be nice to be there on the day.
"The owner rang me this morning and I just had to get in touch with my agent and he put me on it.
"It is all for a good charity, so hopefully the horse can run better than expected. I will try not to get in anyone's way.
"I've not spoken to any of the lads yet. They've not given me any stick yet, but I am sure they will."
The BHA said in a statement on Wednesday evening that 7lb claimer Mangan, who has not yet won a race in Britain, could not take part in the Derby under one of its rules which protects "the best interests of the sport".
With Mangan having never ridden at Epsom nor in a big race like the Derby, the BHA said that her participation would pose an increased "risk" to the welfare of jockeys and horses.
The BHA had, however, said last Sunday that "there are no restrictions in place" to stop Mangan from riding at Epsom, but that race conditions could be discussed "on an ongoing basis, if appropriate".
Diore Lia, a maiden filly who is available at odds of 1,000-1, is trained by Mangan's boss John Jenkins and is owned by Mary Todd.
Todd's brother Richard Aylward bred the horse and has been keen to generate publicity for Great Ormond Street Hospital by running the daughter of Yeats at Epsom.
Aylward said: "She's definitely running and Paddy will be riding her.
"Our filly is the people's champion now and I hope everyone gets behind her."
Aylward feels Mangan has been left "badly scarred" by being unable to ride in the Derby.
He said: "She's in a terrible mess and can't work or anything.
"Poor old Gina is badly scarred from what the BHA has done to her."
Aylward will attempt to try to discuss the Mangan case with the Queen, who will be present at Epsom on Saturday.
He said: "Our story needs telling because I've been left very, very upset about what has gone on and I feel so sorry for Gina.
"The Queen is a patron of Great Ormond Street Hospital and it's my intention to speak to her about what has happened when she comes in the parade ring before the Derby.
"We've had contributions from as far away as America for our charity, and we're hoping it will now take off because of all this that has gone on."
When asked to assess the chances of Diore Lia, Aylward added: "I don't think she'll finish last. She's improving."
Star jockey Ryan Moore said the BHA should be "congratulated" for blocking Mangan's participation in the Derby.
He told Betfair: "More than anything, the BHA has done the correct thing for the horse and jockey, as much as the sport and the other participants in the race.
"In this game you can't take safety for granted, and you would have been asking the horse and jockey to do something at Epsom that they simply weren't equipped to do."
Professional Jockeys Association chief executive Paul Struthers believes the BHA made the "right decision" to stop Mangan riding in the Derby, but felt racing's ruler should not have granted her clearance in the first place.
He said: "I have spoken to Gina (on Thursday morning) and she is obviously very disappointed that she won't be able to ride in the Derby on Saturday.
"The BHA were in an unenviable position and in the circumstances we believe they have taken the right decision, albeit in hindsight it would have been far preferable not to have given Gina the public green light to ride earlier in the week."