Brian and his former fiance Aussie singer Delta Goodrem's relationship came to an end last month after seven years together.
It was after Brian saw photos of Delta and Nick holding hands that he issued his warning.
The ex-Westlife singer tells the Sydney Daily Telegraph, "It's fine; you see it (the photo of Goodrem and Jonas together) and accept it for what it is. It was positive. She looks happy. If she's happy, I don't mind. But there's a warning from me: If anyone hurts her they're dead...
"I wish her all the happiness in the world... We're still really good friends."
Irish singer Brian McFadden and fiancée Delta Goodrem split
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