The horse has developed a whining – a bacterial respiratory infection – after the race.
The infection has led to the start of sepsis, which is “probably a key factor” in the cause of death.
The blood tests carried out on the day of the race indicated that the infection had not been present in the horse on Raceday.
The British Horseracing Authority (BHA) said that the post mortem exam was just a “party” of their process of examining any death and that the death of Celebre d'Allen would be analyzed in detail.
Celebre d'Allen was a 125-1 shot at the National, which was won by Jockey Patrick Mullins on Nick Rockett.
On Tuesday, it was also announced that Mullins received an eight -day ban after his journey was returned to the whip review committee.
The amateur jockey, 35, broke the whip rules during the race, using his whip eight times after the final fence when the leaving race limit is seven.
He will be suspended for eight distinct days, including April 23 and 25.
Allen's death of Celebre caused criticism of animal rights groups, Animal Rising saying that the sport of horse racing was to blame for the death of the horse.
Animal Aid said it was “shameful” to allow a horse's age horse to be mounted in the “most exhausting race in the country”.
The BHA said that there were 24 horses of 13 since 2000 who participated in the Grand National, without previous deaths.
