Closing down and cruising past Minella Indo to win in thrilling fashion, Ireland's sporting golden girl showed more emotion than at any point in her career as she toasted a famous triumph.
"I can't believe it, I don't know what to say," said Blackmore.
"I am so lucky to get to ride all these horses. You can't do it without these horses. Being attached to Henry's yard is unbelievable. I don't know what to say.
"I’ve had so many special days. I wouldn’t swap the Grand National for anything but this is the Gold Cup. I wish I had something better to say right now. I just can’t.
"You have all these plans about how things are going to work out. Racing doesn’t let that happen all the time and for some reason it’s happened to me today. I just can’t explain how lucky I feel.
"I was where I wanted to be at the end and I made sure I didn't go too soon like I did last year. I held onto him a little more than last year and it worked.
"I knew after the second half that I had more horse under me than I had last year and he was amazing.
"When I took out my racing license, I didn't even think I'd be riding at Cheltenham. What's I'm doing now is a dream I never thought would be possible. To win the Gold Cup is something else."
Richard Thompson, of owners Cheveley Park Stud, said: "We’ve been talking about this moment, and it’s happened. It’s absolutely fantastic to win the Gold Cup. Incredible.
"My father would have loved it, he watched the Gold Cup for many years and to actually win it is incredible. I can’t even speak.
"I did feel she was a bit far back, but I knew she had a gameplan – she has totally delivered. What a day for racing.”
Second 12 months ago to fellow Henry de Bromhead-trained runner Minella Indo, the pair reversed that form in style as the 3-1 favourite stormed up the hill to claim a stylish success.
Blackmore, who became the first woman to win the Champion Hurdle and Grand National last season, now has another trophy in her collection and this one clearly meant so much to her.
Racing legend Ruby Walsh saluted Walsh's latest golden moment, as he suggested Blackmore was a gift to racing.
"She is box office," declared Walsh on ITV Sport. "You can see by her reaction what it means to her. What a moment.
"There is no better feeling than winning the Gold Cup. Rachael gave A Plus Tard an incredible ride and this is great for racing. Rachael is wonderful for our industry."