Michaela McAreavey cried out in anguish when she was strangled on her honeymoon in Mauritius, a court heard.
Lawyer Mehdi Manrakhan told a jury in the trial of two men accused of her murder that a witness heard a scuffle taking place in room 1025 at the Legends Hotel.
The prosecutor told the Supreme Court in Port Louis: "He heard a female voice crying and then 'Agh, agh, agh' as if she was in pain."
He claimed the witness - Raj Theekoy - then saw the two men accused of the murder leave the room.
Manrakhan added: "This was a dream honeymoon for John (McAreavey, her husband) and Michaela, which turned into a nightmare."
Defendants Avinash Treebhoowoon and Sandip Moneea deny the charge of premeditated murder.
The prosecutor said McAreavey had returned to their room after his wife, daughter of Tyrone Gaelic football boss Mickey Harte, failed to return from fetching biscuits to have with a cup of tea. He had to get a member of the hotel staff to open the door when no-one answered.
"As soon as John entered room 1025 his worst nightmare began," said Manrakhan.
"In the bathroom John saw Michaela lying senseless in the bathtub."
Manrakhan said medical examinations showed McAreavey died from asphyxiation due to compression of the neck.
"Medical evidence is such that there can be no doubt that Michaela had been brutally killed," he said.