(CNN) -- After months of speculation, one of Formula One's worst kept secrets has finally been confirmed. 

Fernando Alonso, the double world champion who recently left Ferrari, will rejoin McLaren for the 2015 season, which gets underway in March. 

The Spaniard, who won back-to-back world titles with Renault in 2005 and 2006, joins the British team after ending his four-year association with Ferrari. 

He will be partnered by Jenson Button, whose services were retained above Kevin Magnussen, who stays on as a test and reserve driver. 

Between them, Alonso and Button have won three world titles, 47 grands prix and achieved 147 podium finishes from a combined 500 races. 

Now 33, Alonso will be expected to boost McLaren's fortunes after a season which saw it struggle to match the pace set by the all-conquering Mercedes team. 

"Over the past year I have received several offers, some of them really tempting given the current performance of some of the teams that showed interest," he said in a statement. 

"But, more than a year ago, McLaren-Honda contacted me and asked me to take part, in a very active way, in the return of their partnership -- a partnership that dominated the Formula 1 scene for so long." 

Between 1988 and 1992, McLaren and Honda won 44 grands prix out of 80, with Ayrton Senna and Alain Prost winning all but one of the 16 races in one season. 

"I still remember, as a kid, the posters in my wardrobe, my toy cars in which I dreamed I would one day emulate Ayrton, and the kart that my father built for my older sister, and that I ended up falling in love with," Alonso added. 
Who will be his partner?
He will be partnered by Jenson Button