Inside billionaire Warren Buffett's unconventional marriage, which included an open arrangement and 3-way Christmas cards

• Warren Buffett married Susan Thompson in 1952.

• She ultimately left Warren to pursue a singing career, but they remained amicably married until her death in 2004.

• Susan also introduced her husband to Astrid Menks, who became his companion. Buffett and Menks married in 2006.

For much of his life, investment guru Warren Buffett has had a less than conventional marriage.

While he remained married to his first wife Susan from 1952 till her death in 2004, he lived with Astrid Menks. Menks and Buffett didn't tie the knot until 2006, two years after Susan passed away.

But family members said the unusual arrangement worked for all those involved. According to the Daily Mail, the trio would even send out Christmas cards together, signed Warren, Susan, and Astrid.

"Unconventional is not a bad thing," Buffett's daughter Susie Buffett told the New York Times. "More people should have unconventional marriages."

Here's a look inside Warren Buffett's married life: