However, she told the Diary that she hadn't noticed any particular chemistry between the pair when she joined Daithi on the judging panel at the festival two summers ago.
Mary (53) explained how her fellow Rose of Tralee judges were touched when they first learned of the blossoming love story.
"It was unexpected but I think it's really nice. I mean it's a lovely story. He seems very happy so I'm delighted for him," Mary said.
"We were judges together last year and the year before that so I would have been there when he first met her.
"He's not the first high profile presenter to have ended up with a Rose, Ryan Tubridy led the way.
"It's not surprising because they're very eligible young women and let's face it he's a very eligible young man, well relatively young man," she laughed.
Daithi's new lady, Rita was on hand last night to cheer on her man as he took to the stage to present the first of the two selection nights.
The brunette beauty, who hails from Dumont, New Jersey, was determined she would be remaining tight-lipped about her budding romance, however, insisting that she didn't want to steal her other half's thunder on his big night.
Rita (27), who was the first ever New Jersey Rose, had a memorable party piece when she performed Pat Shortt's song Jumbo Breakfast Roll following her television interview with Ray D'Arcy in 2008.
The outgoing character, whose family own a chain of pubs in New Jersey, was spotted bonding with Daithi's proud mother Kathleen following last night's live broadcast.
Nationwide presenter Mary went on to explain how she had offered Daithi some tips ahead of his big debut last night and believes he carried the gig off without a hitch.
Mary, who previously hosted RTE magazine series Open House alongside Marty Whelan, believes that Daithi is the ideal candidate to join Herald columnist Claire Byrne as co-host of the national broadcaster's new afternoon series, Daily Extra.
According to the mum of four: "I think he'll do very well with all of it. We had a chat about it. I did the Eurovision and I just kind of said to him well this is how it is, you get from one commercial break to the next and that's it.
"He's from the area and everyone is thrilled to have him up there on stage. The whole county is rooting for him.
"I think it's nice to see a bit of flirting with the girls. He's certainly good at that.
"He doesn't have long to prepare for the new afternoon show but he'll be a big success, there's no doubt about it," she added.