Former President George W. Bush offered his prayers to Sen. John McCain, R-Ariz., on Thursday after his office revealed he has been diagnosed with brain cancer.

"I called Sen. John McCain this morning to wish him well and encourage him in his fight. Instead, he encouraged me," Bush said in a statement.

"I was impressed by his spirit and determination. He has devoted his life to his country. Thankfully, he is committed to continuing that service. Laura and I pray for our friend to fully recover and quickly return to the Senate, where his voice and leadership are needed. And we send our very best wishes to Cindy and the entire McCain family."

Former Pres. George W. Bush says he called Sen. John McCain "to wish him well and encourage him in his fight. Instead, he encouraged me." pic.twitter.com/9qZGH8GLXu — ABC News (@ABC) July 20, 2017

McCain, 80, recently underwent an operation to remove a blood clot from above his left eye.

According to the Mayo Clinic in Phoenix, Arizona, where he is being treated, tissue extracted during the procedure proved to be cancerous.

McCain and his family continue to review treatment options, including chemotherapy and radiation.

The senator's office said there was no timetable for when he would return to Washington, D.C.

McCain received an outpouring of support from his Republican and Democratic colleagues, as well as President Trump, Vice President Mike Pence, former President Barack Obama, and former Vice President Joe Biden.