"Special visit today with a great friend — and now, a best-selling author," Bush tweeted. "Luckily I had a freshly laundered pair of @BillClinton socks to mark the occasion."
Bush is known for his colorful and animated sock collection and in this photo, the former president showed off a pair of blue and black socks with Clinton's portrait. A smiling Clinton is seen pointing at the socks.
Bush also shared another photo of the pair, along with a lab named Sully, who according to Bush is from America's VetDogs and is the newest member of the Bush family.
Clinton, who co-authored the thriller, "The President Is Missing" with writer James Patterson, is on a book tour that launched earlier this month.
During a visit to Houston last April, Clinton gifted Bush a few pairs of colorful socks, tweeting, "Great to spend time with @GeorgeHWBush & Mrs. Bush in Houston today. We caught up about kids, grandkids, old times and new times. And socks."
And in 2013 Clinton shared a photo of himself with Bush in Maine and remarked that he is "envious" of his fellow former president's "sockswag."
Clinton and the younger Bush reflected on their friendship during while speaking at a Presidential Leadership Scholars graduation ceremony last July, where Bush said Clinton had a humble attitude after defeating his father in the 1992 presidential election.
“I think it starts with Bill Clinton being a person who refused to lord his victory over Dad,” Bush said. “In other words, he was humble in victory, which is very important in dealing with other people.”
In 2014 Clinton tweeted a picture of himself reading the younger Bush's book, "41", a heartfelt tribute to his father and wrote, "Received my copy of #41 by #43, George W. Bush. Touching tribute! #HowAreYouSTILLNotOnTwitter #PresidentialTweeters," noting that Bush 43 was not (and is still not) on Twitter.
Clinton and his wife, former first lady and Democratic presidential candidate Hillary Clinton, both wrote heartfelt tributes to Barbara Bush.
"Barbara Bush was a remarkable woman," the former president tweeted in April. "She had grit & grace, brains & beauty. She was fierce & feisty in support of her family & friends, her country & her causes. She showed us what an honest, vibrant, full life looks like. Hillary and I mourn her passing and bless her memory."