Whatever, I always consider Heathrow to have been a seven runway airport!
Well technically it was, in the sense that the runways were numbered from 1 to 7, even if they were never all in use at the same time.
I must admit that when I first worked at Heathrow in the 70s, I could never understand why 10L/28R was Runway 1, but 10R/28L was Runway 5. When I eventually did some research into LHR's history, all became clear.