British twin brothers Adam and Simon Yates will race together at the Vuelta a Espana for Australian team Mitchelton-Scott.
Simon was scheduled to take part in the final Grand Tour of the season and will be the team's leader in the race.
Adam also decided to ride to add to his experience of competing in multiple big races after a modest Tour de France.
He will ride in support of his 26-year-old sibling in the race, which starts in Malaga on 25 August.
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"The Vuelta a Espana wasn't originally on my program," Adam said.
"But, together with the management, we came to the decision that doing the Vuelta after the Tour would be another good chance to get some experience in riding multiple Grand Tours in one year."
Adam, who was fourth in the 2016 Tour de France as he won the young riders' classification, finished in 29th - more than an hour behind winner Geraint Thomas - in this year's race.
Simon led the Giro d'Italia for 13 days this year before falling away on stage 19 of the race, which was eventually won by fellow British rider Chris Froome.
"My preparation has been very different to the Giro d'Italia because like a few guys that will line up in Spain, I have one eye on the World Championships later this year," Simon said.
"It will be interesting to see how my body responds but, as always, I'll give it my all to achieve a great result."