According to The Sun, Kate has been busy planning the royal bash for weeks and since Harry is a big fan of Ellie's, the Duchess wanted to snap her up for a live performance at the party.
The Royal Wedding, the Invictus Games and now Harry's birthday do... Ellie sure is a hit with the royal family lately!
Back in 2011, the 'Burn' singer famously sang 'Your Song' for Prince William and Kate at their wedding reception and clearly impressed with Ellie's vocals, Harry had the singer booked as one of the acts to perform at the Invictus Games closing ceremony - an international sporting event he hosted over the weekend (11-14 September).
After her performance at the Games, Ellie was spotted backstage sharing a joke and cuddling up to the Prince.
Good friends with Harry, Ellie made sure to catch up with the royal at the event and congratulate him on his organising efforts.
Now, it seems the 27-year-old will join Harry once more for his birthday celebrations, after he turned 30 on Monday (15 September), treating him to his very own acoustic set.
A source told The Sun, Kate was keen to get Ellie to perform as she knows "Harry is a big fan of hers" and on being asked, the singer was quick to say yes to the gig.
Ellie, who is dating McFly star Dougie Poynter, is expected to perform an intimate set for the Prince and his guests and has apparently agreed to sing "whatever Harry fancies hearing" on the night.
Oh, if only we could get our hands on a plus one...
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