The former Miss World was presented with a diamond sparkler worth an estimated €40,000 by a smitten Wes during their holiday on the island of Mauritius.
Rosanna said: "He got down on one knee after a walk on the beach and then we celebrated with the family with a glass of champagne.
"The setting couldn't have been more romantic and special, we are delighted!"
And tweeting this morning, Rosanna still appeared to be coming to terms with the engagement.
"Woke up... Ring still on... Wasn't all a crazy dream!"
Much like his bride to be, Wes is over the moon and paid a tribute to his girlfriend of six years.
"So happy to be engaged to my best friend who I love so much ... party time."
The ring was described as a "big square solitaire on a band of diamonds" and Wes posted up a pic of the ring on his Twitter page, joking how he "hopes she's worth it".
Rosanna wasted little time in sharing the good news with her tight-knit family and friends.
The couple, who holiday on the sun-kissed island with their families every Christmas, have been at the centre of speculation lately as to whether 2013 might be the year they make things official.
And they were inundated with messages from well-wishers after breaking the happy news of their engagement on Twitter and Facebook.
Celebs including Grainne Seoige, Georgia Salpa, Andrea Roche and Brian Kennedy all sent the couple messages of congratulations.
Ever-the-gentleman, Wes had made sure to ask permission from her famous father, Chris de Burgh, prior to asking for the model's hand in marriage.
Wes had the impressive engagement ring -- a cushion-cut ring with old cut, pave-set shoulders -- designed especially for Rosanna.
Wes had been carefully planning his proposal for a number of weeks and waited until the end of their two-week trip to go down on bended knee and surprise her with a sparkler.
The pair had been staying at the luxurious Le Saint Geran Hotel, where they go every year with Rosanna's family, including her dad Chris, mum Diana and her grandmother.
The couple's relationship has gone from strength-to-strength in recent years, with the pair taking the big step of moving in together two years ago in a house in Foxrock.
Wes has also supported Rosanna through the highs and lows of her career and had "no problem" with her decision to pose topless for Playboy last year. She even asked him for help in deciding which pictures to choose for the spread, which hit headlines around the world.