The family of former U.S. Marine Paul Whelan, who has been held in Russia for more than three years, said they now have "a little bit of hope" after learning that the United States has offered a prisoner swap to bring home Whelan as well as another detained American, professional basketball player Brittney Griner.

"The offer that the U.S. government has made -- and extraordinarily made public -- is super. Hopefully the Russian government will take the concessions that have been made and allow Paul to come home," Whelan's twin brother, David Whelan, told Robin Roberts during an interview Thursday on "Good Morning America."

It's the first time the Whelan family has spoken out since U.S. Secretary of State Antony Blinken announced Wednesday that he will hold a call with Russian Foreign Minister Sergey Lavrov "in the coming days." A critical topic of discussion will be securing Whelan and Griner's freedom.

Blinken revealed the U.S. government had already "put a substantial proposal on the table weeks ago to facilitate their release" and remains hopeful for a breakthrough in their cases.