Fr Frank Gelli, who was a curate of St Mary Abbots church in Kensington, West London, close to the Princess Diana's former home at Kensington Palace made the revelations to The Sunday Express.
He said in the months leading up to her death in Paris, the princess began attending the church.
The clergyman claims she stopped him on the way to the gym to ask about marriage.
He said: "She wanted to know if it was possible for two people of different religions to marry. I told her it was.
"As we spoke her telephone range. It was obviously Dodi. Her eyes lit up. As she was leaving she asked me if I would be able to perform the service when she got married. Her love was obvious."
Fr Gelli said Princess Diana called to arrange to meet him at Kensington Pace to share good news once she returned from her holiday with Mohamed Fayed.
However, just days later, Princess Diana and Dodi Fayed died in a crash in a Paris underpass, on August 31st 1997.
Meanwhile, The Channel 4 documentary the late Princess of Wales, has divided opinion among commentators with reviews ranging from "trashy" to "heartbreaking".
The use of controversial video tapes in Diana: In Her Own Words has already been strongly criticised by royal watchers, and Rosa Monckton, one of Diana's closest friends, said it was a "betrayal of her privacy".
But Channel 4 said it gave the Princess a voice and placed it "front and centre" in the run-up to the 20th anniversary of her death in a car crash in Paris on August 31 1997.
The documentary featured Diana speaking candidly and informally about her upbringing, her courtship with the Prince of Wales, her troubled marriage and her public life.
