Sunday's Barclays Premier League London derby between West Ham United and Chelsea is sure to be keenly contested.
However, one man whose loyalties will be split down the middle at Stamford Bridge is former Hammers and Blues winger Peter Brabrook.
Now 75, Brabrook joined Chelsea from school before making his debut at the age of 17 in 1954, ending his first season by winning the Division One championship. After 271 games and appearing for England at the 1958 FIFA World Cup, he joined West Ham for £35,000 in 1962.
The transfer certainly paid-off as Brabrook helped the Hammers to win the FA Cup for the first time in the club's history in 1964. The following season, he helped West Ham to lift the European Cup Winners' Cup, but unfortunately missed the final through injury.
"I was at Chelsea for nine years and played a lot of games," he explained. "I broke into the side at 17 and was a regular up until 1962 when I went to West Ham. I was fortunate enough to play three or four games in the Championship side in 1955 when I was just 17, which was a great honour.
"I have some really good memories of my time at Chelsea and we certainly had some good players - Roy Bentley who played centre forward, a winger called Frank Blunstone and a right-back called Peter Sillett who also played for England. From there, I joined West Ham and some great players like Bobby Moore, Martin Peters, Geoff Hurst and Johnny Byrne.
"I went to Sweden in 1958, to Gothenburg, when I was 20, and I made my England debut when I played in the play-off against the Soviet Union."
Following his retirement from playing, Brabrook took up a role within the Academy of Football, helping to unearth and mould the likes of current Chelsea and England midfielder Frank Lampard and Hammers and former Blues star Joe Cole. He still works for West Ham in a scouting capacity.
Brabrook is positive about the prospects of both of his former clubs, and cannot wait to see his former scholar Lampard in action again.
"I think Chelsea are a good footballing side. I think they are very good. I know a few of them are pushing on a bit from a few years ago when they were winning everything, which obviously hasn't helped, but they are still good players and warrant being in the team.
"I still think they'll be a force to be reckoned with over the next four or five years as long as their owner Mr Abramovich is still there. He is not short of a few bob, so I'm sure he'll put it into the club and help bring them back to where they were.
"It's fantastic for Frank [that he is still playing so well]. He had to work so hard at his game and made himself a player. He's probably near enough the best player who has ever played for Chelsea. I had him in the Academy with a lot of other good players here and Frank was a massive part of it. He's done exceptionally well to make himself a great player.
"Frank always sneaked in and got a goal as a youngster, too. His overall contribution and work-rate and determination to do well and make himself a player were there to see. He was not a ready-made player. Frank made himself a player with the help of his Dad.
"I'm not leaning either way on Sunday - I'm going to sit on the fence! To me, they are two great clubs. I left school to join Chelsea and was there for nine years. Then I went to West Ham in 1962 and had a fantastic time winning the FA Cup in 1964 and being part of the squad that won the European Cup Winners' Cup. It was great to be here with some really top players."