Delays in completing the new Wembley mean Wales and Cardiff's Millennium Stadium will get a welcome windfall.
The Millennium Stadium has benefited as a Wembley alternative
The city, which had been on standby, will now host the 2006 FA Cup final and the Football League play-offs.
"May will be a massive month for Cardiff and Wales," said Millennium Stadium chief executive Paul Sergeant.
Head of tourism for Cardiff Council, Paul Jenkins, added: "We are obviously disappointed for Wembley but we are delighted to welcome the FA Cup back."
Since 2001 Cardiff has benefited from Wembley's redevelopment, with the Millennium Stadium often used as the alternative venue for big sports and music events.
But the crown jewel has always been the FA Cup, with Cardiff gaining millions of pounds and much prestige as host.
Sergeant said he was "ecstatic" at hosting the FA Cup one more time.
"The FA Cup is one of the most prestigious events in the sporting calendar," he told BBC Wales.
"People travel far and wide for it - the hotels will be full, the pubs, the restaurants, the retailers all do well out of it over the course of the weekend.
"Alongside that you've got the play-offs taking place here, that's three other matches that will be in the stadium."
The FA Cup final will be played on 13 May, then the following weekend Cardiff braces itself for domestic European rugby union's showpiece - the Heineken Cup final - on 20 May, with football's Championship play-off final scheduled the following day.
Then the League One and League Two play-off finals arrive on 27 and 28 May to complete a bumper month.
It is estimated the FA Cup final and the Heineken Cup final could each generate more than £30m for the Welsh economy.
"It costs the council to do it but the economic return far outweighs that in terms of returns," Jenkins said.
"Evidence has shown that people come to the FA Cup and then return, using the city for mini-breaks or a holiday destination."
Building work on Wembley has been fraught with difficulties
There should also be a significant benefit for the Welsh Rugby Union, the owner of the Millennium Stadium which is believed to still owe around £50m on its construction costs.
The Football Association and Football League are thought to have negotiated favourable rates for the five-year block booking for the FA Cup and the play-offs.
Sergeant would not be drawn on what the windfall was for the WRU, but did admit it was an improvement for the extra hire.
"Commercial deals are obviously private between ourselves and the Football Association, but it's slightly different from the previous arrangement," Sergeant said.
"The FA took the prudent measure of reserving the Millennium Stadium to stage the FA Cup final way back in August.
"They took some criticism for it at the time, but what a great step it was on their behalf to reserve the place."