He had a moment of doubt when he trotted out on the turf in Dublin 4 for his senior international debut, asking if he belonged there.
Within minutes, it was clear that Jack Byrne was no impostor. At the end of the game, and his 30-minute cameo, he had the cheers of the Dublin crowd and words of praise from his manager ringing in his ears.
"I think I proved to myself on Tuesday night, as I didn't know," says Byrne, asked about making that step up from being a prodigy who had travelled much but delivered little in the previous two years, before a move to Shamrock Rovers led to his revival.
"I am going out there for my first cap - never mind the manager who is a lot more experienced than me, I was going out there thinking 'can I play at this level' as I had never done it before.
"It's only when you are out there, you get your first touch and your normal game takes over and you feel comfortable, it's a normal game of football. Suddenly a goal goes in, the crowd cheer and you are taken back a bit. I am standing in the middle of the Aviva here, it's crazy.
"I came on as No. 10, to try and affect the game, get in shots and crosses, and that's what I tried to do, play my normal game. I didn't try and do anything I wouldn't normally do playing for Shamrock Rovers. If it was enough, it was enough. If it wasn't, it wasn't."
Byrne even had his own fan club made up of family and friends in the crowd, Byrne slightly embarrassed to reveal what was on the specially-made banner they had brought. "Give It A Lash Jack," he admits, with a slight reluctance.
Doubts have plagued Byrne's career since he started making waves as a teen but some of those who encountered him along the way never doubted his ability.
"He can definitely play in the Premier League, I'm telling you," former Manchester United man Wes Brown said at a media event in Dublin yesterday: the pair were team-mates during Byrne's unhappy spell at Blackburn in 2016.
"I used to train with him every day and he is that sort of player - he is aware of everything. If anything, at Blackburn, some of the things he was doing, the other players weren't on the same level.
"He'd do it early and in the Championship they are not necessarily ready for early, they want to play a bit more. He was definitely a player that you'd think: if he uses his talent right, he'd be fantastic."
Talent aside, Byrne also has reputation for over-confidence and admits that the man he is now, at 23, is different from Jack Byrne the teenager. Even Brown saw that at Ewood Park.
"He's very confident, 100pc he was like that, and sometimes that was his downfall," Brown explains.
"But it was never in a nasty way, I think he knows the ability he's got. But sometimes - and we were struggling at the time - the manager won't put the little guy, the magician guy, in. He'll put in players who will work and tackle. Jack is not exactly that player."
Byrne appears to be very happy back home in Dublin and may have done enough against Bulgaria to earn a place in the squad when Ireland duty resumes next month, but the man from Ballybough says he hasn't changed.
He says he didn't look at his mobile phone after the game on Tuesday night. "I spoke to the people close to me I was able to speak to, the rest I didn't entertain," he says.
"It was the same, people texting me and I didn't have their numbers: they're not looking for tickets when we are playing Waterford at home on a Tuesday night. Nothing changes for me, I will keep doing the same thing.
"When your outside life is going well, your football life is going well, and when your football life is going well, your outside life is going well.
"It's trying to find a happy medium. It's easier said than done because you have nights like Tuesday and you're up, and then you lose a game on Friday for Rovers and you're back down there. It's about staying in the middle and I haven't been too good at that in the last couple of years so I'm working on that."