Two lifelong friends have just found out they're actually much more than that - they're biological brothers.
Alan Robinson and Walter Macfarlane, from Hawaii, have been close friends for six decades.
Only 15 months apart, the pair bonded over football in Honolulu in sixth grade. Mr Robinson was adopted, and Mr MacFarlane didn't know his father.
It was DNA matching website Ancestry.com that brought them answers years later, and right in time for Christmas, local television station KHON2 reports.
At the top of Mr MacFarlane's list of DNA matches online was the username Robi737. "Robi" is Alan's nickname, and he used to fly Boeing 737s for Aloha Airlines, KHON2 reports.
That's when they realised they were both using the same website, both searching for answers.
"It was a shock," Mr Macfarlane told KHON2, to realise then they had the same mother.
The two have now made plans to travel and retire together.