Mitchell popped the question to Breeds in April as they shared a four-day break on Hayman Island, Queensland to celebrate his birthday. He had been preparing for the proposal for three months.
© Channel 5
© Channel 5
The pair, who play Summer Bay's Romeo Smith and Ruby Buckton, confirmed their news in the latest issue of New Idea magazine.
Mitchell told the publication: "Honestly, it was one of the most difficult things I've ever done in my life. I had the element of surprise - I didn't tell anyone what I was planning, not a soul, not even my parents.
"But pretending there was nothing special on my mind for three months before I actually asked her to marry me - that was the best acting I've ever done!"
Recalling the proposal, Breeds commented: "I turned around and there was Luke on one knee with a ring box in his hand. My jaw just hit the ground. I was so surprised I forgot to say 'yes' at first!"
© Channel 5
© Channel 5
The couple first met in May 2009 shortly after Mitchell had been cast in Home and Away. They initially became friends before embarking on a relationship.
Home and Away fans have also seen Romeo and Ruby have an on-off romance in the soap's storylines.
Breeds added: "I don't want a long engagement. There's a film out at the moment, The Five Year Engagement, but I don't think that's how we're going to roll!"
Home and Away airs weekdays at 6pm on Channel 5 in the UK and weekdays at 7pm on Network Seven in Australia.
