His song played over the loud speaker and he walked out to a noisy crowd at the packed Rotorua Girls' High School Arena.
Little did the crowd know what was to come.
King and fellow Rotorua local Ra Wiki battled out one of the fights of the night.
After the umpire lifted King's hand in victory, following three hard-hitting rounds, King started to unfold his master plan.
He was given the microphone and thanked his girlfriend for her support in the build-up to the event, calling her into the ring.
Gasps and cheers started to ring across the arena as the crowd sensed something was up.
King's boxing coach handed him a little box and he knelt on one knee, catching Monro in full surprise. The cheers and whistles lifted around the arena.
Such was the shock of the whole scenario, it took until after the pair had got out of the ring for Monro to say yes, or more precisely, "of course".
"I was humming and harring about it right up to about a week before, and Tanya [Warren] was like 'just do it'," King said.
King said the nerves before the fight were focused on the proposal rather than the fight, and it actually helped him take his mind off things trading blows with Wiki. Later in the night, Monro explained she had no idea what was coming.
"Even when he called me into the ring I was not sure what was going on."
She said during their years together King had often caught her by surprise with romantic events.
Monro said the pair had met in school during their years at Western Heights High School and she liked him ever since.
"I've always had a crush on him since high school and we got together in Australia about three years ago."
King revealed he would have gone through with the proposal even if he had lost, and was simply hoping he did not get knocked out.
The RotoVegas World Championships corporate fight night featured 13 fights on Saturday night, with most participants getting in the ring for the first time.
All the fighters the Rotorua Daily Post spoke to on the night were over the moon about getting in the ring.
New Zealand boxing legend David Tua was also on hand on Saturday, bringing down one of his fighters from his Auckland gym to take on Rotorua's Jared Gray. Gray lost the feature fight in a very close match with Alex Fa'anunu.
RotoVegas Boxing Gym organised the event and confirmed they would be holding it again about the same time next year, with a possible smaller event in August.
-Results from the RotoVegas World Championships corporate fight night on Saturday:
Sililo Levae defeated Aaron Morrison; Racheal Hatcher defeated Maylene Mereoiti; Graham Black defeated Karl John; Tammy Nicholls defeated Te Aroha Wihapi; Olivia Adams defeated Elle Reid; George Gilmore defeated Regan Feek; Ashleigh Gray defeated Lisa Duff; Nicole Harvey defeated Vickey Eggleton; Carl Gage defeated Joe Dorset; Ryan Petch defeated Nathan Toi; Denton Grimes defeated Aubrey Rikihana; Slade King defeated Ra Wiki; Alex Fa'anunu defeated Jared Gray.
