He was under the guidance of Frank Lampard last season with the Rams, and the newly-appointed Chelsea boss wanted to keep Tomori at the Bridge this season.
For Tomori, he wasn't preferred in the opening few games, but come Sheffield United at home at the end of August, the 21-year-old defender was given his chance, and he hasn't looked back since.
He has been phenomenal at the back for the Blues, despite a few errors which comes with lack of experience, and the centre-back will only continue to grow.
Frank Lampard has been constant in his praise for the defender, and last week it was Gareth Southgate seeing something in the youngster.
The England squad was revealed for the Euro 2020 qualifiers against Bulgaria and Czech Republic and Fikayo Tomori was included.
He joined his fellow Chelsea cohort of Tammy Abraham, Mason Mount and Ross Barkley who all made the cut.
Speaking after the 2-1 win over Southampton, Tomori revealed he didn't expect to be playing for England at the start of the season: "Yeah, I wasn’t really expecting it. I came in this season trying to improve myself and give myself the best chance to play in the Premier League.
"Playing for Chelsea is what I’ve been doing since I was seven years old, so it’s nice it’s happened this way," Tomori said as he continues to flourish at the heart of the Chelsea defense.
"Having the manager say that about you is nice and that’s what you want. I know he has that faith in me and he’s showed me that faith last year and this year.
"I’ve just tried to work hard and I knew coming back for pre-season I would have to take myself up a couple of levels and I was going to have to learn from other people. So, that’s what I’ve been doing and it’s nice he’s saying that, but I want to carry on and keep improving."
But prior to being called up to the England squad for the first time, Tomori did have other options which included Canada and Nigeria, but he gave his reasons for choosing the Three Lions for his international career.
"England is such a big nation, as well as Nigeria and Canada," Tomori said. "So I think I was going to be happy with whoever called me up - but it’s nice it is England.
"It wasn’t England all the way. I had certain people and certain things that I had to consider. I spoke to my family and people that I care about it and that’s the decision I came to. So, when England came calling, it was difficult to say no.
"It was just more of a thing I was waiting for a call-up because the last international break I didn't get a call-up from anyone. This international break, I was waiting for a call-up and England called me up.
"It’s been a good week. Nice to get the England call-up, but winning in Lille and today, it’s been a good week. The manager [Frank Lampard] told me in the changing room after the Lille game [about his England call-up] so I knew a day before and I had to keep it a secret.
"I told my family and then it got announced on Thursday. Not at all [did I see it coming]. The manager told me and I was like ‘oh’. It was a nice feeling. I’d say so [that it came quicker than I expected].
"Last season, I wasn’t expecting to be there but I never really put a limit on saying I couldn’t do it. It was just more a case of I’ve got to give my best for my club and wherever I was going to be playing week in, week out and try to get in the squad wherever I was. It is obviously good I am here and now, to be in the England squad, it’s a mad turnaround for myself."
The Chelsea youngster touched on the tactics and systems which Frank Lampard has used, with the Blues boss prone to changing it up this season depending on the opposition.
"It makes it a lot easier because the manager outlines what he wants from us and we try not to change it up too much. It’s still the same principles of we want to press, we want to work hard for each other.
"Regardless of the shape, those are the fundamentals and the basics of what we want to be doing," Tomori continued. "It makes it easier if we switch from a three to a four. Sometimes you have to adapt to the opposition but most of the time we want to play our own game."
He will now be hoping to get his first cap for the Three Lions, with the preferred option being against Bulgaria at the national stadium at Wembley.