The FA have confirmed the final will not be moved to another date and Kensington Palace say they will factor in the game as part of their wedding planning.
The date has been set for the occasion at St George's Chapel at Windsor Castle on the same day as the famous cup decider at Wembley.
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A Kensington Palace spokesman said: "We are aware of it and we haven't announced times yet. It will be considered as part of the further planning."
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The Gunners also beat William's beloved Aston Villa in the 2015 final, where he handed losers medals to his Villa heroes.
And it has thrown into doubt whether FA president Prince William - Harry's brother - will present the trophy to the winning captain as usual.
Last Updated: 15/12/17 5:09pm
Asked why a Saturday, the spokesman said: "They felt it would give the public the greatest opportunity to watch, come out, support and get involved."
The wedding of Prince Harry and Meghan Markle has been announced for May 19 next year - and it clashes with the FA Cup final.
No decision has yet been made by the FA over who will hand over the silverware. Harry is also a supporter of Arsenal, who won the FA Cup last season and were handed their winners medals by William; the Duke of Cambridge.