The FA Cup cast its spell upon the Savages while they were out shopping for groceries.

Reading midfielder Charlie was strolling the aisles of the Marks & Spencer foodhall with his girlfriend when his phone began to buzz. He remembered it was first-round draw day. 

He fished out the phone, saw the cascade of messages and realised, as they like to say in M&S, this was not just any FA Cup draw. He called his dad.

Peterborough United boss Robbie was in the Co-op. He had stopped on his way back to the rented lodgings he describes as a 'little annexe in someone's garden' and was rummaging through the ready meals in search of a spaghetti bolognese for one when he answered.

'The reception in Peterborough isn't great, it kept cutting out,' Robbie tells Daily Mail Sport. 'Charlie said: "You won't believe the draw." I thought he was going to say Forest Green. Or Macclesfield. I didn't think about Reading. He said: "You've got us." I just went: "Oh no."'

They were on a collision course from the moment Robbie left Forest Green for the Posh job last month. The teams were scheduled to meet in League One next month at Reading but the FA Cup draw caught them off guard.

And while they were both at great pains to stress that Saturday's tie at London Road, screened live on TNT Sports, is about Peterborough and Reading not their little family gathering, they can appreciate the fuss.

'Football is a beautiful game, it brings people together and creates rivalries,' says Charlie. 'This week it's created a rivalry in our family. I'm not sure who my mum, brother, grandparents and cousins will support but there's no better time for them to have a half-and-half scarf.'

For Robbie, the beauty of the occasion is yet to unfurl itself. 'It's going to be horrible,' he says. 'Every time I watch my sons play, I'm anxious. I'm nervous. I want them to do well. If they give the ball away and the other team attack, I've got butterflies thinking, "Please don't score".

'This will be the first time I hope my son doesn't have an impact, which is a horrible feeling. People keep telling me it's great. I've got to say it's not great, it's horrible. Usually we speak every day and I've not been able to speak to him all week because I don't want to put him in a position where anything gets out and anyone can point a finger at him.

'I don't want it to be billed as Savage v Savage because it's not. Charlie might not play but if he plays and makes a mistake and we score the winner, so be it. If he plays and scores the winner, well, wow.' 

Robbie puffs out his cheeks and widens his eyes as he considers this scenario. 'We've got to win for Peterborough United,' he adds.

Ironically, it was a passion relit by coaching his sons which tempted the former Leicester, Birmingham and Blackburn midfielder out of the comfort of his media work and into coaching. Savage helped out with his youngest son Freddie's Under 13s team in the Timperley and District Junior Sunday League.

'Standing out at training on a Tuesday and Thursday night,' says Robbie. 'Sunday morning, putting the nets up. I've been that dad. In the first season we were hammered 13-0, but we built a team and won a lot of things.'

Two years ago, Charlie and Freddie implored their father to follow his heart and make the switch from sporting director to manager at Macclesfield in the Northern Premier League.

'Even back then, he said one day he'd manage against me,' Charlie tells Daily Mail Sport. 'I was in League One and he was in Step Three and I'm thinking, "Well, give it a few years", but he always gets where he wants to get to.

'He's a competitor. He wants to win, wants to succeed. Even with my little brother's team it hurt him to lose in Sunday morning grassroots football. That's something inside him and it won't change. 

'He will want to beat us. Unfortunately for him, I'm the same. I want to win. There might be an awkward car journey home.'

Charlie's memories of his father playing football are from Derby, the last stop of a 15-year professional career which started at Manchester United and took in seven different clubs, as well as 39 Wales caps. 'I remember seeing his long hair, scurrying around the pitch,' says the 23-year-old. 'Throwing his arms up and shouting at the refs.'

Like his dad, Charlie also came through United's youth ranks and made one first-team appearance, as a substitute at the age of 18 against Young Boys in the Champions League. It was an unforgettable night for Robbie, who was on co-commentary duty with a lump in his throat.

'He'll always have that on me,' says Robbie. 'All I ever wanted to do from 14 to 19 was play for one minute in Manchester United's first team. It didn't happen and he's done it. His name is on the wall at Carrington and mine isn't.

'I'm so glad his name is there instead of mine. You want the best for your sons. I'm proud of both my sons.'

Freddie is studying for an economics degree at the University of Manchester. Charlie left United for Reading four years ago and now has 175 senior appearances and three Wales caps under his belt and a reputation in his own right.

'He's got a great left foot, passing range and incredible running ability,' says Robbie. 'He's intelligent. Nine As in his GCSEs. He doesn't drink, he lives his life 24 hours a day, seven days a week to be a footballer. He's a down-to-earth, humble kid.

'He was so brave to go and play senior football when he had three years left at Manchester United, and it's paid off. He played 45 games last season. He hasn't started a league game this season but hasn't sulked.

'I was a sulker, as Martin O'Neill and Nigel Clough (who coached Savage at Leicester and Derby respectively) will tell you. If that was me, my body language would be negative, but he's got a great attitude. And I've tried to tell him now he has to train harder than ever and conduct himself in the right way.'

If Robbie is a guiding light and inspiration for Charlie, vital information flows both ways for an aspiring manager with a young team.

'The mindset of a Millennial is completely different to when I played,' says the 52-year-old Posh boss. 'If they're not in the team or the manager has shouted at them, they go home to an apartment where they live alone away from their families, isolated from 2pm to 7am with all that time to think about it.

'We have to understand their vulnerabilities on and off the pitch. Charlie has been through that so without knowing it, he's made me a better manager. I try to think about what's best for my players, what I'd want a manager to do for Charlie in that situation.'

Being the Son of Sav cannot be easy. Not only the added scrutiny and expectation, and accusations doors have been opened for him by a famous and influential father, but also in a world where footballers are too often considered fair game for abuse whether inside the stadium or online.

'It's there in all forms of life,' admits Charlie. 'Maybe people subconsciously want me to fail a little bit more because of who he is. I get it. Football is a game and my dad is a divisive figure inside that game. 

'He gives it out and he can take it and, unfortunately, it has become part of his life to be on the receiving end. Sometimes the abuse goes too far. People forget he's a human not just a football personality.

'But I wouldn't change who he is. I wouldn't change having him as my dad, I'm very proud of him.'