After years of bemoaning Tupou's at-times questionable scrummaging for the Reds while he was coaching the ACT Brumbies, McKellar is chuffed to have the powerhouse prop in his corner for Saturday night's spicy derby at Suncorp Stadium.
"I've always had nothing but admiration and respect for 'Nela'," McKellar said on Thursday.
"Coaches are funny people, aren't they?
"You need to twist and turn and and see how you can help things, sway things in your team's direction, but he's always been a destructive scrummager and when he gets it right, he's as good as anyone in the world.
"So it's nice to have him as our tighthead and not have to deal with him as the opposition tighthead, that's for sure."
McKellar hasn't noticed any big change in Tupou's behaviour as he prepares to lock horns with his old side, having been front and centre for the Reds for 88 games before defecting to the Melbourne Rebels and now the Waratahs.
"He's just treating it like any other week. I think Taniela's experienced enough now to understand that," said the Tahs mentor.
"You can't let the emotion get the better of you early in the week. It's important at 6.30 Queensland time on Saturday evening that he's ready to go.
"I'm sure he's excited but he's just going about his preparation like he would for any game."
It won't be long after 6.30 on Saturday night that Tupou can expect to feel the pressure from his old teammates, with Reds hooker Matt Faesler promising some good-natured needle to be headed the Wallabies star's way.
Faessler is expecting a blinder from Tupou and says the Reds can't afford to let him have his way with them.
"Nela's quite familiar with Suncorp and a lot of the guys. It's going to be funny playing against him," he said.Â
"I have no doubt he'll put his stamp on the game. No doubt there will be some barbs at scrum time but personally I just like to focus on playing.
"Talk can wait until after the game."
Saying and telling his charges it's a "privilege" to be involved in an interstate rivalry stretching back to 1882, McKellar had cheekily branded the Reds "the best team in the comp" last Saturday.
And even when reminded the Reds were humbled 43-19 by the Crusaders the following day, he insisted his unbeaten Waratahs would have their work cut out beating the arch-enemies in Brisbane.
"I thought for periods (against the Crusaders) they looked like the best team in the comp," he said.
"When they get their game going, they're very good.
"They're certainly not the first or the last team that will go to Christchurch and have a tough day and there were glimpses throughout that game where you can see how dangerous they are."
The Waratahs will again be without Joseph-Aukuso Suaalii as well as skipper and scrumhalf Jake Gordon, who has joined the superstar back on the sidelines with a knee injury.
While Gordon is expected to miss about a month, McKellar believes Suaalii is a chance is to return from a foot injury for next week's round-six clash home with the Brumbies in Sydney.
