Up For Review fell at the first fence in the race with ITV Sport and Racing Post reporting that he was put down after suffering a serious injury.
It is the first fatality in the race since the deaths of Synchronised and According to Pete in 2012.
ITV presenter Ed Chamberlain said: “It’s bad news with regards to Up for Review, who fell at the first fence and, I’m sad to report, suffered a fatal injury.
“All our thoughts go to trainer Willie Mullins, Danny Mullins who rode Up for Review and poor Graham Wylie, who is one of the nicest men in racing and has just had awful luck of late.
“And also our thoughts for Will Ingram, who looked after Up for Review and I imagine he was his pride and joy.
“This is a sport and race that has a trapdoor to despair, it does break hearts, but it also makes legends.”
General Principle was also hurt, though the injuries are only superficial.
Racing Post said: “General Principle has returned in the horse ambulance but reportedly sustained only superficial injuries.”
Two horses died at Aintree on Friday with Crucial Role and Forest Des Aigles both losing their lives.
There have been 13 deaths at the Grand National since the turn of the millennium.
Horse racing fans took to social media to hail Up For Review following the news of his death.
One posted: “Up For Review has sadly died following a fatal injury at the first fence. RIP. #GrandNational2019”
While another commented: “Spare a thought for Graham Wylie. Two horses lost at Cheltenham and Up For Review today.”
And a third wrote: “Awful awful awful news about Up for Review #GrandNational2019.”
In total, 19 of the 40 runners finished the Grand National.
Tiger Roll became the first horse since Red Rum in the 1970s to win the race in successive years.
Grand National result
1. Tiger Roll
2. Magic of Light
4. Walk in the Mill