Newcastle striker Aleksandar Mitrovic says becoming a father has forced him to grow up: I smashed a train window with a rock I hurled from a bridge... I was so stupid

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Aleksandar Mitrovic counts to seven. He is illustrating how he has matured since becoming a father.

‘When I first signed for Newcastle, I was still a boy. If I lost my temper on the pitch then I could not even count to one,’ says the striker who was sent off just 16 minutes into his Premier League home debut. ‘Now, I get to six, sometimes seven’.

Mitrovic, you suspect, will never make it to 10. Even the birth of son Luka 17 months ago and the impeding arrival of a baby daughter will not entirely tame the temperamental Serb, who confesses that football saved him from a life he would rather not imagine.

Aleksandar Mitrovic insists he has grown up after becoming a father for the first time

The 22-year-old striker admits he was stupid at times during his younger years 

‘My father tells me I would have been a criminal or a kick-boxer,’ he says with a mischievous smile as we sit in the sun following a gruelling pre-season session. A group of fans wait nearby for an autograph.

‘But fatherhood has changed me - a lot. I try to do everything for my son so that, when he grows up, he can say that he was proud of his father.

‘Sometimes before, you would get bored or lose focus, now there is always something to push me hard. I have become a man.’

Mitrovic is reflecting on his journey, one which has taken him from Smederevo in the former Yugoslavia and via Partizan Belgrade to Anderlecht in Belgium and then to Tyneside in a £14.5million move two years ago.

Still just 22 years old, his point is this - he is a changed man, he deserves another shot at the Premier League and he wants that chance with Newcastle.

For now, though, he takes us back to his childhood. It is there that a sense of misadventure led to the scrapes which have shaped him. He will use such memories to guide his own children.

Mitrovic was in action during Newcastle's 2-0 victory over Hellas Verona on Sunday

Mitrovic poses for a photo with his partner Kristina and their seven-month old son Luka

‘The most trouble I was ever in was when we were dropping rocks at the train as it came towards the bridge,’ he starts. ‘Everyone did it, but it was mine which smashed the window. The train had to stop.

‘I ran and ran all the way home. My parents were mad. “Why always you?” they shouted at me. I thought I was just unlucky. Looking back, I shouldn’t have been doing it.

‘But I was always making stupid decisions and getting in trouble. If someone said, “You can’t go there, don’t jump off that”, I would do exactly the opposite, I was naughty.’

Mitrovic’s parents - Ivica and Natasa - tried to channel their son’s adrenaline and devilment. They turned to karate. He liked physical combat, after all.

‘It wasn’t for me, I didn’t like the rules,’ he says, and it makes perfect sense. ‘I wanted to be free of all that.’

Mitrovic needed something which allowed him to express himself but at the same time instilled discipline and took him off the streets.

The forward has been impressing during pre-season and is ready for the Premier League

‘They took me to football and they realised I had a talent,’ he says. ‘I could be aggressive but I was also good with the ball. I watched Alan Shearer - he was my hero.

‘At times I didn’t want to go to practice, I wanted to be with my friends. But as I got older I loved scoring goals. Football saved me.’

And it is his goals return which Mitrovic uses to defend himself against the doubters, of which he fears manager Rafa Benitez is perhaps one.

‘I came here very young for a big transfer fee, I think people can forget that,’ he says, and it is true.

‘But look, I scored nine goals in my first season in the Premier League, in one of the worst teams which was relegated. That is not bad.

‘The Premier League is the hardest in the world. I think I am getting stronger, cleverer and knowing how to play this league.

Mitrovic congratulates team-mate Christian Atsu after his goal at St James' Park

‘I hope the decision is taken so I can stay here. I have to show so much more to the people in England. My best years are still to come.’

Mitrovic has 97 career goals - more than Harry Kane at the same age - and is a cult hero at St James’ Park, yet he splits opinion like no other player.

He lives with his girlfriend, Kristina, on the same road as Newcastle legend Shearer in the leafy parish of Ponteland.

But if a gang of youngsters in black and white shirts are ever spotted on the estate, it is Mitrovic’s house around which they gather.

‘That is nice,’ he says. ‘It is not a problem. They sing my song - ‘Mitro’s on fire’. This is a special place to be a footballer, it is crazy.’

If the chorus kicks in after Luka’s bed-time then perhaps Mitrovic would start to count. Not that his son is one for sleeping.

The Serb scored four goals in 25 Championship appearances last season

‘He is like me when I was young - for 24 hours he wants to play,’ he says. ‘He is kicking a ball, he is kicking me, he is kicking everything. Sometimes it’s hard, but you always find energy for him.

‘I want him to do the right things when he grows up, and not some of the things I did. I know there will be problems - he is my son - I know what is coming.

‘Only now I understand my parents when they told me why they cared so much.’

Off the pitch, Mitrovic is learning fast. Now he has to prove his newfound maturity on it. Maybe one day he will get to 10 after all.