When Glasgow Warriors host Ulster in the Pro14 semi-final at Scotstoun on Friday night, poignancy as well as passion is guaranteed. Somebody is going to finish their night by saying goodbye.

Depending on who loses, it's either going to be Stuart Hogg bidding farewell to Glasgow after nine years - next stop Exeter - or Rory Best and Darren Cave with a so long to Ulster after a combined 27 years - next stop retirement from club rugby.

It's going to be loud and attritional and emotional no matter how you cut it. Three titans of their surroundings leaving the stage and the likes of Sam Johnson only really getting started.

"This is where you want to be," says the Glasgow and Scotland centre. "Ulster are a great team. The last time we played them [in early April] we won 30-7 but Tommy Seymour pulled off two brilliant bits of defence to deny them two certain tries, so if they go in that's 30-21 and people are remembering it differently."

Ulster did not have Rory Best that night. They did not have Iain Henderson either. That's two leaders and two Lions right there. "It's going to be a great game," says Johnson. "They have massive athletes and Rory is one of the best leaders of men in the world.

"They'll be trying desperately to make sure that Friday isn't his last game for Ulster in the same way we'll be trying desperately to make sure it isn't Hoggy's last game for Glasgow. We haven't spoken about it as a group, but it's there in the subconscious. Everybody knows it.

"I've learned a lot of stuff from Hoggy - the way he conducts himself on and off the pitch, his standards, his dedication to making himself better and the impact that has had on me. You watch him working harder and that makes you work harder as well. I always knew I could play the game but it was only when I came to Glasgow that I realised that I wasn't taking it as seriously as I should have been.

"Playing alongside him gives you so much confidence. You know that if you can give him some quick, clean pill then magic is going to happen. We want to give him the best send-off, not at Scotstoun but at Celtic Park in the final."

'A sheltered boy, quiet and laidback'

Four years ago these same teams met at the same venue at the same stage of the competition and Glasgow won with a late sweep of Finn Russell's boot. Johnson was just packing his bags in Ipswich, Queensland to come to Scotland at the time. "A sheltered boy," he says of his younger self. "Quiet and laidback and just turned 22. A little bit nervous but kind of excited at the same time.

"My parents, my two sisters and my brother are all in Queensland and, yeah, you wish you could see them more. Everyone has their own journey in life, though, don't they? Sorry, I don't want to be too philosophical about it, but I'm okay about being away from Australia. My life is very much here now.

"When I came over first it was the World Cup in England and I was cheering for Australia. I still had that in me. It's long gone now. In 2015, it was the first time out of my comfort zone. I packed everything up and moved to the other side of the world and it was a shock.

"The second night I was here I looked out of my window and there was this guy standing outside the door of the building with blood streaming down his face. He was in a bad way. The police arrived. Loads of cars. It turned out that the fellow had been attacked by a guy with a machete. I'm this kid who's been living with his mum and dad all his life and suddenly I feel like a million miles from home.

"That was the last time I saw anything like that. Glasgow is home now. My girlfriend is Scottish and we're looking to start a life together here. I'm so grateful for everything that's happened to me. It took me a while to get used to things at the start. I found it difficult to talk to people. I just sat in the corner. I didn't come over as a star signing so nobody paid any attention to me. I've had to work hard and I'm proud of what I've done so far. Nobody in Australia knew who I was back then. Nobody in Australia knows who I am now, to be honest."

That might have been true up until this spring, but it's not true anymore. His first Scotland cap against Italy will have given him some kind of profile in Australia. His try against Ireland will have enhanced his reputation further, but it was his score against England that will have had rugby fans in Australia wondering how they missed out on this guy.

Johnson calls the Six Nations a "whirlwind, an experience like I've never known before." And he adds: "So many more eyes on you. So many more followers on Instagram after the try at Twickenham."

'We know what's coming, but we're in a good head space'

Clever, quick and skilful, when he scored under the sticks that evening he thought he had won the game. The dart through a gap in the English defence - "you could have driven a bus through the hole" - the step off his right foot to get around Jack Nowell, the right-hand fend of Elliot Daly, the bowling over of one Englishman, then another and then the touch down. It looked like history in the making.

"I'd watched some of the Italy versus France game earlier in the day and I saw the Italy centre [Marco Zanon] going over in the corner only for Damian Penaud to knock the ball out of his hands as he was about to score. When I crossed the England line that image sprung into my head and I thought to myself, do not drop this ball'. I thought we'd done it. It was an awesome feeling."

In the end, he had cause (again) to remind himself of something that Jonny Gray had told him about a year earlier. "Jonny said something really good in the car one day," Johnson explains. "It was a simple thought, but very, very true. He said, 'you've never made it in this game'. And he's right. Just when you think you've made it, England score or you lose your form or you get injured and lose your place.

"I'm playing 12 against Ulster but I know that loads of others are chomping at the bit to get that jersey. You can't rest, you can't rely on reputation. That stuck with me. We're in a privileged position as rugby players but it can be taken away very quickly. That thought helps me. I have a bit of fear at the moment of joining the real world. I don't want to. I want to ride this wave for as long as possible."

White horses of a different kind are heading his way at Scotstoun. Ulster have not won a trophy in 13 years and their survivors from Glasgow, 2015 - Best, Henderson, Cave, Louis Ludik, Stuart McCloskey, Rob Herring - have not forgotten what it felt like that night. 'We know what's coming, but we're in a good head space," adds Johnson. "This will be a proper battle, though."