The 24-year-old met the young royal when he and wife Catherine saw her perform at Radio 1's Big Weekend last year.
In an interview with the UK's Evening Standard magazine, Ellie said: 'Prince William was just really gushing, and like: 'I really enjoyed the show'. He is so nice, just genuinely the nicest human being.'
She added that an aide from Buckingham Palace later went to watch her rehearse for a performance but she kept it from her band.
Goulding said: 'I kept it a secret - I just told them to be on their best behaviour.'
Her booking for the wedding was later confirmed by Buckingham Palace and it's claimed she performed a cover of Elton John's track Your Song.