Bobs Worth, trained by Nicky Henderson and ridden by Barry Geraghty, won the Betfred Cheltenham Gold Cup providing Henderson with a second win in three years under the jockey.
The Duke and Duchess of Cambridge had headed to the races for the Gold Cup showdown.
Kate, who is five months pregnant, hid her bump under a blush coloured Joseph coat, accessorised with a dark chocolate brown bow trimmed Betty Boop hat from Lock & Co, brown gloves, brown patterned tights and knee high brown boots.
In maintaining his unbeaten record at the track, Bobs Worth, the 11-4 favourite, outstayed Tony McCoy and Sir Des Champs up the Cheltenham hill.
Long Run, Henderson's winner from 2011, attempted to make all for his amateur jockey Sam Waley-Cohen but faded into third.
Silviniaco Conti was a faller at the third-last when still going well in the hands of Ruby Walsh.
Bobs Worth crept quietly into contention under Geraghty but there were still five in with a realistic chance coming down the hill.
Results - Cheltenham Gold Cup
Cheltenham 3:20 Bobs Worth (B J Geraghty) 11-4 Fav Sir Des Champs (A P McCoy) 4-1 Long Run (Mr S Waley-Cohen) 7-2 9 ran Also: 16-1 The Giant Bolster 4th Tote: win £3.50 places £1.50 £1.90 £1.70 £5.00 Bobs Worth Tote Exacta: Bobs Worth £13.30
The Giant Bolster, last year's runner-up, was clinging on to the coat tails of the leaders but a slow jump at the second-last cost him his chance of glory.
When Bobs Worth and Sir Des Champs passed Long Run it was left to the two new kids on the block to fight out the finish and although Bobs Worth went clear, he began to idle on the run-in.
For a few strides it looked as if McCoy, a late replacement for the injured Davy Russell, would galvanise Willie Mullins' charge, but he could not get back on terms and went down by seven lengths in the end with a further two back to Long Run.
Geraghty said: "I'd love to be happier. All we can think about is John Thomas McNamara. We just hope and pray to God he's OK.
"This is a brilliant, he is a gorgeous horse and he has a great attitude.
"He never travelled, he struggled on that ground, but he kept fighting.
"I knew three out I had five or six lengths to find, but I thought I had a good chance.
"He's as game as a lion and he loves the job."
Henderson, celebrating his 50th Festival winner, said: "It's all a bit of a blur. You have to gather your thoughts. We've been at it a good few years.
"Both horses were fantastic and everybody has done a hell of a job. Bobs Worth hasn't run since the Hennessy and Long Run hasn't run since the King George, so it was all down to what we did at home and we did it as a team.
"I have to thank them all. They were brilliant."
Henderson added: "I was worried about the ground but they are two really brave horses and you just have to take what you get.
"You take take anything away from Long run, Sam (Waley-Cohen) was going hammer and tongs with AP (McCoy) and he wasn't intimidated.
"It's been a long week and a long old season, we've had to do the work at home with them and the staff have had to put up with me.
"Neither of them have run much (this season), it's only three weeks to Aintree. I wouldn't rule it out for Bobs Worth but he's had a hard race and I'll have a look at him in a week.
"I could definitely see Long Run going to Aintree."