Romantic Shaun Murphy (21) was three metres deep at the time, enjoying a shark dive in the 4.5 million litre Underwater Safari display, when he held up a sign that read, 'Sharon Hunter...Will you marry me? P.s. Your dad approves'.
Sharon (20), from Alloa, was standing in the tunnel and signalled yes from the other side of the glass.
She told the Advertiser, "I was shocked, gobsmacked and embarrassed - as I don't like public attention."
Shaun jokingly added, "If she said no, I would have just fed her to the sharks."
The couple, who have been dating since 2006, first met as part of the Argyll & Sutherland Highlanders ACF.
Shaun said, "She hated me at first, but then after the ACF annual camp I grew on her."
Shaun, who is a director of Castle PC Repairs Ltd, planned to propose at Christmas until he was given the shark dive experience for his 21st birthday.
He said, "I thought it would make for a memorable present and a bigger surprise that she wouldn't forget."
Taking the advice of Sharon's best friend Laura Willocks, Shaun sought out Sharon's father's permission to which he received the seal of approval.
The amorous lad then liaised with the team at Sea World to ensure everything went smoothly and was delighted when the Stirling University nursing student said yes.
He declared, "I was more nervous about diving with the sharks."
The couple now plan to enjoy their engagement and will wait until after Sharon has graduated before setting a firm date for the wedding sometime in 2014.
Shaun added, "I would like to thank my family for the amazing experience for my 21st birthday, Deep Sea World for outstanding service, Laura Willocks for keeping the secret, and everyone else involved."