Postpublished at 19:33 Greenwich Mean Time 8 February 2017
Leicester v Derby (19:45 GMT)
Match of the Day has kicked off - and our pundits aren't impressed by the Leicester starting XI...
Ndidi and Gray score fantastic extra-time goals for Leicester
Foxes will travel to League One side Millwall in the fifth round
Watch clips of goals and key incidents on this page
Both sides named weakened teams (10 changes for Leicester, eight for Derby)
Jonathan Jurejko
Leicester v Derby (19:45 GMT)
Match of the Day has kicked off - and our pundits aren't impressed by the Leicester starting XI...
Leicester v Derby (19:45 GMT)
Statistical proof that it has been an unhappy for Leicester (and Leyton Orient) fans...
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#getinspired
Wednesday's always a big day for university sport and we're urging students to sign up for the FA People's Cup - the country's biggest free five-a-side tournament.
Watch England women's team members Siobhan Chamberlain, Izzy Christiansen and Demi Stokes explain how university kick-started their football careers, and why you should get involved in the People's Cup, then check out all the information you need to sign up, here.
The deadline for registration is 19 February, so don't miss out - join the party now!
Meanwhile, any students out there? Sick of assignments? Sick of hangovers? We've got the perfect thing for you...
Leicester v Derby (19:45 GMT)
If that little refresh hasn't whetted your appetite then nothing will.
Leicester v Derby (19:45 GMT)
So what happened last time out? You can't have forgotten. We witnessed one of THE great own goals.
Darren Bent shanked his way into FA Cup folklore in the original tie - or at least the Derby striker would have done had he not dug himself, and the team, out of the hole with the equaliser.
Craig Bryson put the Championship side ahead when he fired in, only for Leicester to force a replay when Wes Morgan headed in a late corner for 2-2.
Watch Bent's embarrassing moment below, and head here for the match report.
#bbcfacup
On the back of Claudio Ranieri allegedly banning chicken burgers, we want to know what infuriating rules have been cooked up by your boss.
Rich Rimington: A (glad to say) former boss banned any more than one cup of tea during the first hour in the office every day...
Tweet #bbcfacup or text 81111. Keep them clean.
Leicester v Derby (19:45 GMT)
Want to watch the game on the telly? Listen to the radio? Or maybe all three (because you're obviously already reading here and aren't going to ditch us)?
Our BBC Radio 5 live colleagues are already up and running at the King Power Stadium, with local lad Gary Lineker presenting the BBC One coverage from 19:30 GMT.
He's joined by Alan Shearer, former Leicester manager Martin O'Neill and ex-Foxes and Derby midfielder Robbie Savage.
Hope Sav is wearing a half-and-half scarf.
Leicester v Derby (19:45 GMT)
Manager Steve McClaren makes eight changes to the Derby starting XI that lost 1-0 at Championship rivals Newcastle last weekend.
Goalkeeper Jonathan Mitchell is handed only his third senior start and forward Nick Blackman makes his first start since August.
Leicester v Derby (19:45 GMT)
The Foxes make 10 changes from the side that lost 3-0 at home to Manchester United on Sunday.
However, midfielders Riyad Mahrez and Danny Drinkwater and forwards Shinji Okazaki and Islam Slimani are on the bench.
Jamie Vardy? He is sat at home in front of the fire. Possibly. He isn't in the squad anyway.
Leicester v Derby (19:45 GMT)
If you haven't seen the team news yet, then here it is...
Leicester v Derby (19:45 GMT)
Not many fans have braved the Leicester chill yet. They're downstairs in the King Power concourses warming up with that mouth-burning combo of milky tea and a chicken balti pie no doubt.
Or maybe they've seen the team news and decided to stay at home in front of the fire.
Leicester v Derby (19:45 GMT)
A trip to Millwall might not be everyone's cup of tea, but that is what Leicester and Derby are aiming to clinch tonight.
The League One play-off hopefuls will host either of these East Midlands rivals in the fifth round on Saturday, 18 February.
Who knows, this might the year that Grandad out of Only Fools and Horses is proved right..., external
Leicester v Derby (19:45 GMT)
Derby County manager Steve McClaren: "Obviously we've made a few changes, four or five are coming back from injury.
"The message is 'go out and do the job, keep it simple and fight for 95 minutes'. We're here to win the game.
"I didn't want to make eight changes. If the game was last night the team would have been totally different.
"I've got injuries and I've got people who can't play three games in a week. I've had to pick the team accordingly. I think it is a great opportunity for the players coming back and the squad."
Leicester v Derby (19:45 GMT)
Steve McClaren has also just been talking in a typically-honest manner to the BBC cameras - after making sure he knew from the Match of the Day producers when they would be going to the dressing room cameras. He didn't want any of his players being caught "picking their nose". Quite right.
#bbcfacup
At least someone is up for the cup....
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Leicester v Derby (19:45 GMT)
Claudio Ranieri has been collared by our interviewer in the King Power tunnel. And the Leicester manager has been asked about his team selection...
"I wanted to protect some players and give an opportunity to the other players for them to show their strengths," says the Italian.
"It will be difficult but I had to do this. I have a big battle on Sunday and that is more important. We are ready to fight."
#bbcfacup
Has Claudio Ranieri banned post-match chicken burgers, external for his players? He says he hasn't ruffled any feathers by hatching such a plan. (Sorry.)
But we're not letting that small denial get in the way of our evening fun. Using this true-or-not story as our inspiration, we want to know what infuriating rules have been lumped on you by your boss.
Ever been told you can't eat bananas in the office because your gaffer hates them? Or maybe the boss has banned red clothes because it is the colour of his team's arch-rivals.
I'm sure you can do better. Tweet #bbcfacup or text 81111. Keep them clean.
Leicester v Derby (19:45 GMT)
The last time Leicester made so many changes? The 5-0 defeat at Porto. Now I'm not saying Derby are as good as Porto but...
Leicester v Derby (19:45 GMT)
Magic of the cup, eh.