Tim Cook just made a funny joke about marriage in front of 20,000 Cisco employees

Getty Images/Chip Somodevilla

Famously single Apple CEO Tim Cook.

Cisco's annual sales conference in Las Vegas hosted an unusual guest: Tim Cook.

The sales conference is where Cisco gathers its throng of 20,000 sales people and fires them up in the new fiscal year. CEO Chuck Robbins drove the crowd wild by launching the conference with a big announcement, that Cisco and Apple$4 work better on Cisco networks.

And then Tim Cook shocked the crowd when he strolled on stage. 

So Cisco trotted out its own celebrity exec, former CEO John Chambers who retired last month to become executive chairman, to interview Cook. (It says something about $4 that he did this interview, not the newly crowned CEO, Robbins.)

Chambers, who married his high-school sweetheart Elaine, talked about how corporate partnerships are like marriages.

Cook, who is openly gay and extremely private about his love life, quipped, "I can't talk about marriage much."

Cook also said he hoped this new partnership lived longer than he will.

 And he said that it takes two to partner.

That remark is a clue that Cook does have a clue what marriage, or at least a long-term relationship, is all about.