The Valencia striker, 23, was not even aware Del Bosque was naming his squad on Friday for Euro 2016 qualifiers against Slovakia and Luxembourg.
"I was taking a shower and Paco Alcacer told me. I didn't know that the list was being announced at 12:30 today," Rodrigo revealed.
But the former Real Madrid youth product was suitably delighted to be in the mix to represent his country, as they continue their path towards France in two years.
"This is one of the happiest days of my life," he said.
"I've experienced some really happy moments, but this is one of the best.
"It's something I've been looking forward to for a long time and although I'm calm about it on the surface, inside me I'm jumping for joy."
Despite spending time at The Santiago Bernabeu, Rodrigo credited time with Portuguese powerhouse Benfica - where he scored 27 league goals in 67 appearances - as crucial to his rise.
"My mobile phone is full of calls and messages, although I've not had chance to reply to anyone yet, I'm thankful to them all," he said.
"My years at Benfica have also helped me get here. I'm grateful to all the teams I've played for."
Rodrigo joins Bayern Munich left-back Juan Bernat as the potential debutants for the Euro qualifiers, the first of which in Zilina on Thursday.
Del Bosque explained his reasons for selecting the pair.
"Bernat is included because of his characteristics, for all that he can offer on the left flank, both at the back and going forward," the coach said.
"Rodrigo is also playing out wide and as a second striker. Both of them can be Spain players for many years to come."
Bayern coach Pep Guardiola said Bernat's recent form was worthy of a Spanish call-up, with the former Barcelona boss picking the left-sided player in all of Bayern's 10 competitive matches so far this season.
"I'm delighted for him because he's played very well in the last three or four matches," Guardiola said.
"It's great news for him and for Bayern."
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