The youthful Neath captain has been a Wales lock since he was thrown in against New Zealand as a 20-year-old in 1989; 24 next Saturday, he is at once the youngest in the pack who face Scotland at Murrayfield this afternoon and, with 13 caps, their most experienced member.
The young man himself shrugs it off, but it would be a heavy burden for even the most gnarled of veterans to bear. And, whatever he may say, Llewellyn has had so many more dark days than golden visions during his Wales career that the sudden expectancy thrust upon him threatens to get out of hand.
It has been occasioned by the commanding performance at the line-out which, one could argue, saved the game for Wales when they beat England 10-9 at Cardiff Arms Park a fortnight ago. Time and again Llewellyn elevated his 6ft 6in in critical defensive situations to deny his 6ft 10in opposite number, Martin Bayfield.
'I came off feeling I'd done reasonably well but then everyone kept telling me I was man of the match,' he said. 'When I watched the video I'd done slightly better than I thought. I'm not in one of the more glamorous positions where you get credit for winning matches, so it was very satisfying.'
Llewellyn knows to enjoy it while he may, because most of his Wales career has been punctuated by doubts. 'There have been times when I've thought some of the criticism of me was unfair but also there have been times when I've been mistakenly praised.
'I'm glad everyone seems to think kindly of me at the moment but I realise that it would just take one bad game for me to be back where I was. You have to enjoy the ups while you can because if things change people will soon start sticking the knife in.'
Llewellyn is the solitary survivor of the sizeable Neath contingent on whom Ron Waldron contentiously relied when he was Wales coach, the 1991 Welsh humiliation on and off the field in Brisbane still burnished on Llewellyn's memory by its regularity as a conversation topic.
Llewellyn played as a replacement in the 63-6 defeat and was at the epicentre of the internal Welsh ructions that disfigured the post-match function. At this distance, perhaps we can put it down to inexperience, though that was not how it seemed at the time.
'It's disappointing that Neath don't have more players involved with the Welsh team but we are going through a rebuilding phase and selections are always made from the most successful clubs,' he said. 'It was no different before. Neath being the most successful club at the time, they had more players in the squad.
'I don't really like to talk about the tour of Australia but everyone still goes on about it. It wasn't just the results. Everyone knows there wasn't a good feeling among certain players on the tour. If something is going wrong and everyone is together, you can put it right. But if there's backbiting, you can't do anything.'
And so it came to pass. Wales retreated in disarray; Waldron, ailing and exhausted, resigned; and Alan Davies became coach. Henceforward Welsh players were not instructed what to do but invited to work it out for themselves. Add this to the influence wrought by his election as Neath captain and the transformation of Llewellyn, player and person, is palpable.
'The captaincy has thrust extra responsibility on his shoulders - which has given him another dimension in that he now has to think of things other than his own personal performance,' Leighton Davies, his coach at Neath, said. 'That responsibility has shown itself in a more mature person developing.
'He still has a few rough edges but he has been thrust into a position where he has to lead by example and earn the respect of his players - both of which he has done. At 23, he has a good six or eight years in him at top level and I've told him he is certainly one of the people who could end up as captain of Wales.'
All of which has brought a new assertiveness to Llewellyn's play, in keeping with the philosophy Alan Davies has sought to inculcate. 'I've become more demanding of the people around me in the line-out. I'm the guy who has to win the ball and they have to do what I want in order to win it. It works well at Neath and it's starting to work well with Wales.
'If we're practising and something isn't benefiting me, we don't do it - simple as that. This is the big thing about Alan: a lot of the answers come from the players. We take the responsibility. He's excellent, a very different coach from any I've previously been used to.
'Sometimes it can be a long way of doing it but, instead of telling the players what they should be doing, he tends to ask questions and get the answers from the players. He knows the answers all along but he wants you to work it out for yourself.'
When Llewellyn first made the Welsh team, it was on the strength of his contribution for Neath against the emergent All Black Ian Jones in 1989. He rejects the idea that this was premature promotion but freely admits there were mistakes along the way. In the 1991 championship, for instance, he was roundly criticised for the inertia of his displays against England and Scotland.
He explains: 'I'd had a serious pelvic injury when I was picked against England. I convinced myself I was OK but I knew my body wasn't as good as it had been before. I played and partially popped a rib cartilage in the last couple of minutes. Going up to Scotland, I'd been passed fit and I thought I was right, but on the field I knew I wasn't and I was dropped after that game. I won't make the same mistake again.'
It probably had something to do with the callowness of youth, something Llewellyn has been forced to shed as captain of his club - and also, as Leighton Davies pointed out, by 'working (as a fitter at Port Talbot steelworks, where he has had a complimentary meal each day since the England game) in an industry where you have to grow up quickly'. In other words, the boy is becoming a man.