The Clondalkin-born beauty (22) bumped into the Hell's Kitchen star during a night out in Pure nightclub with some of her fellow pageant contestants and reveals how she was left a little "starstruck" after meeting him.
She said she had a "great night" partying away in the VIP venue and has certainly had a whirlwind few weeks, meeting her 88 rivals and attending a string of events in the run-up to the December 19 final.
The raven-haired Dubliner, whose dream is to become a Victoria's Secret model, flew over to the millionaire's playground in Nevada at the start of this month and is staying in the Planet Hollywood resort and casino resort in the heart of Vegas.
She said: "I've never seen so many gorgeous girls, there's some very tough competition!"
Her agent Andrea Roche explained how the advertising and marketing communications graduate is realistic about her chances of winning the overall Miss Universe title.
"She is having a fantastic time. The standard this year is off the charts so she doesn't think she'll win but she is loving the whole experience," she told the Diary.
And Adrienne will no doubt get an added boost next week when her long-term boyfriend Luke Kennedy flies over. She has been dating the soldier for more than six years and he's making sure to give her some moral support, along with her equally-proud mum Maeve.
The keen fitness fan is now keeping her fingers crossed that she'll make it through to the semi-finals of the competition. She'll compete in the national costume show tomorrow night, ahead of the grand finale, which will be co-hosted by E! News anchor and Andy Cohen.
Grammy-award winners Train will perform at the event, which will see last year's winner Leila Lopes handing over her crown to her successor. Prior to winning the Irish title last month, which saw her competing as Miss Dandelion, she had modelled part-time for two years as she got her teeth stuck into the industry.