His boss, Harris County Judge Ed Emmett says he got the news last Thursday.
"He came to visit with me and I was taken aback, shall we say, I had not heard anything about it. And I was literally walking out the office door when he had a conversation. And that conversation I'll keep relatively private, but I said hey are you sure you want to do this and he said yes, and then we talked about a letter."
That letter was submitted to Commissioner's Court this week. In it, Bettencourt outlines his intention to resign.
Bettencourt says he didn't have a hard time deciding to leave the county.
"You either decide you're going to stay in government service for the rest of your career, or you're going to try to get back to the private sector before you get too old and somebody may not want to give you an offer like this. And for me, the excitement of being able to run my own company, but not only watch the money, but actually do it on a more capitalistic basis as opposed to making sure we don't lose any of the $5 billion down here, had great appeal."
Bettencourt says a lot has changed for him in the last year since he filed for re-election, and that the private sector is now the best place for him.
That leaves the Commissioners Court with the task of appointing someone to fill his unexpired term until the 2010 election cycle.
Judge Emmett says he already has a list of more than 25 people to be considered, and he anticipates that list will grow.
"I want to find the most qualified person to run the office of tax assessor-collector. And it's not necessarily a political figure. It's not necessarily somebody who's run and won another office or run and lost another office.Î¾Î¾It's whoever I think can best run the office of tax assessor-collector for Harris County and a county of almost four million people."
Several names are already being bandied about as possibilities, including former District Clerk Theresa Chang and former Houston Councilmembers Mark Ellis and Gabe Vasquez.
But ultimately it comes down to a collaborative decision by commissioners.
Whomever gets the job, Bettencourt is confident of what they'll find when they take over the office.
"I think that any appointed tax assessor would find the office in incredibly good shape. And I think I've done my fiduciary duty over ten years to make the tax office the best in the country."
Bettencourt intends to step down on December 23rd, but by state law is required to remain in the position until a successor is officially verified and sworn in.
Laurie Johnson. KUHF-Houston Public Radio News.