When I look at what Romelu Lukaku is doing at this World Cup, I am so proud.

Romelu is a player and person I have a special relationship with. I have known him for seven years, since he first came to Chelsea at the age of 18 in 2011, and we are really close.

He is more than my very good friend, he is a kid I love and he is like my younger brother - someone I have always tried to help.

I know things have not always been easy for him but the reason he is doing so well in Russia is down to the character he has shown throughout his career and the hard work he has put in to get here.

Drogba and Lukaku were both at Chelsea in 2011-12 but never played together - Drogba came off the bench to replace Lukaku on the final day of the season

Of course, Belgium are creating lots of chances for him - if you have Eden Hazard, Kevin de Bruyne and Dries Mertens behind you, then as a striker you know they will provide food for you.

But the rest is down to him. I had service like that at Chelsea, and I always thought to myself: 'If you don't eat well now, then you are the one responsible.'

What I mean by that is if you have got people delivering good balls to you then if you miss it is your fault - and that is the mentality Romelu has got too.

As we have seen, he is not missing now - he has scored four goals from five shots in the two games he has played so far - and I would put that down to the fact that, as a player, he is a perfectionist.

If you have a desire to always improve like he does, then in the end it pays off.

'At the start he was raw - he had to work on everything'

The first time I spoke to Romelu, he was a young boy and still at Anderlecht.

My friend Vincent Kompany put him on the phone and Romelu told me he was a big Chelsea fan and I was his idol - he had my name on the back of his shirt, and a poster of me on his wall.

A few years later, the boy was with us, sitting next to me in the Chelsea dressing room.

I got him that space, because he was supposed to be the next Chelsea striker, so I wanted him to feel comfortable, to learn and understand the spirit of the team from me.

I wanted to pass on to him my advice and experience of the club - that is why he was there.

Right from the start, he had to work hard. I remember when he first came to the club he was not doing the full training sessions sometimes - they would take him to one side and make him work on his first touch, his passing - everything.

When he was young he was very raw. Powerful and physical, yes - always.

I always challenged him and told him that he needed to get leaner and he would be a different player - faster, and more agile at moving and turning.

He has done that. When I look at the player he is now and the one he was seven years ago, there is a big difference. If you go through the different parts of his game, there is quality everywhere.

'He does not lack confidence, he just wants to improve'

It did not work out for Romelu at Chelsea but we have stayed in touch all this time, and we still speak a lot. I'm pleased that he says I was able to help him.

He would always call me for advice, or to ask how to do things differently, but that was never down to a lack of confidence - just his desire to improve.

As I said in my TV analysis after he scored twice against Tunisia, we have talked a lot about the runs he makes, the angles he takes and his footwork when he is through on goal.

The short steps he took before he scored his first goal in that game were just like the ones a tennis player takes just before they hit the ball, and they give you more accuracy.

That was great to see but, when I talked to him after Belgium had played Panama, we spoke about one of the chances he had and I told him what he could have done better in that situation than the touch he took with his left foot.

Romelu explained he was trying to beat the defender but I said you need to focus on your first touch so it would have been better to control with your right and then get in front of the defender that way.

He watched it again and said: "Oh yeah, yeah, yeah - you were right."

There is an example of how much he wants to learn. When you hear that, you can tell he is going to reach the top. He is not there yet, but he is almost there.

'Mourinho understood the boy has become a man'

I have heard Romelu say his determination to win is the most important thing he has learned from me, and I think it is a big part of him as a player.

Like I always say, you can be at 70% of your potential but you still have to give 100% of that because it can be enough to win a game.

Part of that is your attitude. For me there was always a difference between being in the dressing room and being around the lads - joking and having fun - and the moment I stepped out on the field.

I changed, and I think he noticed that when he watched me when he was young. He respected that and I can see he is the same now too. He showed that at Manchester United last season.

I also know United manager Jose Mourinho well, of course, from our time at Chelsea and I can see why he got the best out of Romelu at Old Trafford.

I think Jose understood when he signed him for United last year that the boy has become a man. He was mature and ready for a challenge like playing for a club like United.

Romelu did so well because he has got the confidence of the manager, but also because he is at the age where he knows how to pay that confidence back.

'With Lukaku in form, Belgium have a chance'

I am still challenging him, for example to get more goals for United next season than the 27 he got last season, and to get the Golden Boot at this World Cup too.

We do not always talk about work, though. I have been to see him at Belgium's training camp in Moscow and we did not speak seriously then.

I know his team-mates Eden Hazard, Marouane Fellaini and their assistant coach Thierry Henry as well, and it was nice to speak to them all about everything and nothing.

It was just normal chat between friends, making jokes about players and watching Croatia's win over Argentina at the same time.

We were just having fun and it was clear that Romelu and the Belgium squad are in a good place, not just playing well and winning games.

That is one of the reasons I am backing them to do so well at this tournament, and with Romelu in this sort of form, they definitely have a chance.

Didier Drogba was speaking to BBC Sport's Chris Bevan in Moscow.