"I want to thank the organisers and the wonderful crowd who made all the difference as we cycled by, helping to spur me on to finish the gruelling 100 miles in a respectable eight hours.
"Huge congratulations to everyone who took part
"RideLondon is now firmly on the map as one of the greatest cycling events in the world."
Mr Johnson, who battled with a puncture to complete the challenge in just over eight hours, was taking part in one of a number of events this weekend in what was billed as the UK's largest festival of cycling.
Mr Johnson said: "This is a great day for cycling, and for this city.
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Officers were given the touching letter at Brixton Station while they were on a reassurance patrol after yesterday's attack
The 52-year-old had previous convictions for violence but was not on the anti-terror watchlist.
In a statement Charlton Athletic said: Keith was a true hero who will be greatly missed by all the Charlton family and everyone at the club.