The top four finishers at the Tour de France – Froome, Nairo Quintana, Alejandro Valverde and Vincenzo Nibali – will all line up at the start in Marbella on August 22, as will Fabio Aru and Mikel Landa, who finished second and third at the Giro d’Italia.
"If you had told me before the start of the year, I wouldn’t have believed it. It’s the icing on the cake," Guillén told Spanish newspaper AS. "It’s good that so many important riders have thought to make more of a big year. Froome’s decision is fantastic for the Vuelta and for cycling."
Defending champion Alberto Contador, who won the Giro and finished fifth at the Tour, is the most high-profile absentee from the Vuelta field, but Guillén will surely feel that Froome’s presence is a suitable compensation.
Since the race switched to its current Autumn slot on the calendar 20 years ago, only one reigning Tour champion before Froome has gone on to ride the Vuelta in the same season, Carlos Sastre in 2008. Sastre went on to finish that Vuelta in third place behind Contador.
Backed by a Sky team that seems likely to include Sergio Henao and Geraint Thomas, Froome will have designs on final overall victory, having placed second at the Vuelta in 2011, when he lost out by just 13 seconds to Juan José Cobo, and last year, when he placed second behind Contador. Froome also finished in fourth place at the 2012 Vuelta.
"He likes the race and the country too. The Spanish crowds like him and he feels comfortable here," Guillén said. "And the sporting challenge will have carried weight too. He knows the Vuelta and only one rider has come here after winning the Tour, Carlos Sastre in 2008."
Twelve months ago, Contador made a dramatic late decision to ride the Vuelta after recovering from a fractured tibia sustained at the Tour, but the Spaniard has already brought the curtain down on his 2015 season.
"It’s a shame but it’s understandable," Guillén said. "He gave everything in the Giro and the Tour. The only chance of him [riding the Vuelta] was if he had won in France too and was going for the treble. We’ll try in 2016."
Along with the top finishers from the Giro and Tour, the Vuelta field will also feature Tejay van Garderen (BMC) and Joaquim Rodriguez (Katusha), while the parcours is a typically selective one, with the first summit finish arriving at Caminito del Rey on the second day.
"You could say that it’s a very ‘Vuelta’ Vuelta, with an early finish at altitude and several spicy days," Guillén said. "Things will become clearer from Andorra but everybody will have think about his strategy for the Burgos time trial [on stage 17 – ed.], and I hope we can get there without the overall being decided."