BBC Sport unpicks the issues behind the switch in time of Saturday's big race at Aintree.
In 1997 a bomb scare cause the race to be postponed for two days
Q. Why did officials decide to move the race back 25 minutes?
A. The Royal wedding is taking place on Saturday, after being postponed from Friday because of the Pope's funeral.
With both the Royal wedding and Grand National scheduled for BBC One, it was feared the wedding coverage would eat into the big race build-up.
So a compromise was reached, with the earlier Aintree races shown on BBC Two before racing coverage switches to the main channel at 1530 (all times BST).
The National has been put back from 1545 to 1610.
Will other races be affected?
A. Yes, on Saturday. The schedule has been changed so one of the races, a handicap hurdle initially planned for after the Grand National, has been moved forward to 1450.
The Grand National will be the fifth race in a seven-race programme.
Aintree's three-day National meeting starts on Thursday, and the opening two days are not affected.
Q. If the Royal wedding is at 1230 why the need to delay the race at all?
A. The civil wedding ceremony of Prince Charles and Camilla Parker Bowles takes place at 1230 in Windsor's Guildhall.
It is followed by a church blessing in St George's Chapel at Windsor Castle, which the Queen will attend.
The blessing will take place at 1430, and the couple may not emerge until about 1515, which would be just half an hour before the race's original scheduled start time.
Q. But why not just have the race on BBC Two?
A. When asked, a BBC spokeswoman refused to comment on suggestions the broadcaster has an agreement in its contract with Aintree that the National must be shown on the main channel.
She said: "We are very pleased that members of the public will be able to enjoy both events to the full."
With a domestic audience of about 10 million viewers, the National is regarded as one of the jewels in the sporting calendar.
The Grand National is always screened on BBC One and it was felt this tradition should continue.
And the BBC wants to give the race its usual comprehensive build-up.
Q. Has the Grand National always been at 1545?
Runners take about 10 minutes to complete the 4.5-mile course
A. It has become the established start time in recent years, although the 1997 Grand National was disrupted by an IRA bomb scare and was postponed until 1700 on the Monday.
One theory is it offers football supporters at matches the chance to catch the action during half-time.
However, with the first period of many games not finishing until nearer 1550 or 1555 these days, that argument carries less weight.
Supporters can, of course, follow radio commentary on BBC Five Live.
Q. Will the time affect the BBC's coverage of the National?
A. It should certainly make things interesting when Premiership matches and other football fixtures are coming to a climax.
If the race starts on time, in its new slot, then the winner should pass the post at about 1620.
That leaves a maximum of probably 25 minutes to fit in reaction, analysis, comment, a re-run of the race and the breakdown of how your selection fared.
Q. Will delaying it by 25 minutes affect viewing figures?
A. Almost certainly.
One school of thought believes the National will be hit by the delay as people will either be not interested in the Royal wedding, or confused by the change.
But it is quite possible the wedding will attract an audience of about 20 million, and many of these viewers may stick with the BBC One coverage.
Prince Edward's wedding, which was a more low-key event than the current affair, had an audience of 10m.
Before news of Saturday's delay, one spread betting firm reckoned the nuptials would attract 18m viewers, with the National being watched by 13m
Will the Queen have time to get a bet on?!
Not in person, as she has to host a reception for the happy couple. Her Majesty could always ring the Royal bookmaker, whoever that might be.
After all, Clan Royal, Royal Auclair and It Takes Time are among the leading contenders.
She might also send an assistant into Windsor where a well-known bookmaker is opening a new branch in Windsor this week.
They have even organised for lookalikes of the prince and Mrs Parker Bowles to be on hand for the opening ceremony on Thursday.
And whatever happens, bookmakers will be celebrating.
They believe an extra 25 minutes for punters to have a later wager will bring in an additional £2.5m.