More than 1,000 cyclists joined seven-time Tour de France winner Lance Armstrong this evening for a spin through Dublin's Phoenix Park.
Mr Armstrong who is in Dublin for a three-day cancer summit announced the event on Twitter this morning.
'Good morning Dublin. Who wants to ride this afternoon? I do. 5:30pm @ the roundabout of Fountain Rd and Chesterfield Ave. See you there,' he tweeted.
He sparked speculation earlier in the week about a bike ride through the streets of Dublin, when he remarked on his Twitter page that he 'sure would like to go for a ride' through Europe's largest urban park.
From more than an hour before the start of this evening's cycle, streams of cyclists poured into the park - many wearing suits.
Traffic backed up from the start point, a few hundred yards from the zoo and Garda HQ, down to Parkgate Street and the edge of the quays.
Mounted gardaí were on duty to keep taffic moving in the park.
Last week, Mr Armstrong caused similar havoc in a Scottish town when he decided to invite the public to join him on an afternoon bike ride.
Around 200 people gathered in the centre of Paisley, Renfrewshire, to applaud, cheer, photograph and cycle with him there.
Mr Armstrong, a testicular cancer survivor, is hosting a cancer conference in Ireland involving world health experts and researchers as well as politicians from around the globe.
