Mr Weather, who teaches English in China, said he got the idea to propose at the castle from Ms Allen's parents. He picked the tower, overlooking Otago Peninsula, as the place to say the words.
"I asked her to turn around and look at the sea because I wanted to read a poem to her and I proposed within the lyrics of the poem I wrote. She immediately and thankfully accepted the proposal," he said.
He wanted to thank Ms Allen's family and the staff at the castle for helping make "the day as special as it was".
The proposal came after a whirlwind romance, with the pair - who first met in the United States in 2006 - only becoming a couple in November.
The pair hoped to tie the knot in July in the US.