The former lovers will meet across a crowded laboratory at the RDS.
Supergeek Ryan and superbrain Aoibhinn have only been seen once together publicly since their split, when he took her to his book launch in October.
The pair broke up last year, following an 18-month relationship.
Running into an ex may fill most people with dread, but these two will have the added pressure of prying eyes when they both descend on the RDS for the BT Young Scientist Exhibition, the Herald can reveal.
Aoibhinn (27), who is a physics teacher, is presenting the annual exhibition for the fifth consecutive year, and her former beau has regularly broadcast from the fair for his radio show.
Tubridy (36) will be on site recording his radio show on Thursday and Aoibhinn will be making several appearances throughout the week as part of her duties as master of ceremonies alongside Aidan Power.
Although Ryan and Aoibhinn confused fans with their on-off status, this Thursday celebrity watchers will see first-hand a face-to-face reunion.
Rumours first emerged that the couple's romance was on the rocks when Tubridy showed up solo to several big events, including the Electric Picnic festival back in September.
The presenter was there to chair a debate, but his usually supportive girlfriend was nowhere in sight and hadn't been snapped on Ryan's arm since last May.
Aoibhinn was a tower of strength for Ryan as he paid a final tribute to his old pal Gerry Ryan last year, when the couple faced the full glare of the media for the first time in their relationship.
Ryan has two children from his marriage to RTE producer Anne Marie Power and initially shunned red-carpet appearances with Aoibhinn.
However, they later became slightly more comfortable being photographed as a couple and occasionally commented on their relationship. But Ryan made no secret of his desire to keep their relationship away from the glare of the media spotlight.
"I understand people's interest but I suppose I was brought up in a way that would not have been impressed by somebody who mouths off about their relationships. In the months that we've been seeing each other we've only gone out once to a public function.
"I find it embarrassing to divulge stuff because a little bit of what I am should be kept to myself. I'm not scared of having my picture taken with Aoibhinn. I just don't want people to think that I'm looking for extra attention.
"I am very protective of her and of us."