CINCINNATI -- This one could sting for a long time.

Left tackle Andrew Whitworth was expected to play his entire career in Cincinnati. On the opening day of free agency, he's on his way to Los Angeles to sign with the Rams.

Whitworth is getting a three-year, $36 million contract with the Rams that includes $15 million guaranteed -- with $2.5 million guaranteed in the second year -- according to ESPN's Adam Schefter.

The Bengals' start to free agency already looked bleak before the signing period, which officially starts at 4 p.m. Thursday.

Now they have a hole at left tackle and a huge void in their locker room.

The Bengals wanted to keep Whitworth, and he wanted to return to Cincinnati. So why didn’t it happen?

It seemed the Bengals targeted Whitworth as their first priority among their free agents, a group that also includes Kevin Zeitler and Dre Kirkpatrick.

But it was a head-scratching, and perhaps telling, sign that the first major signing of free agency for Cincinnati was not Whitworth, but wide receiver Brandon LaFell.

It wasn't that the Bengals didn't try. A source close to the negotiations said they were competitive in their offers, but the gap between the money offered in the first year and the amount of fully guaranteed money the second year was just too great.

Whitworth, now 35 and potentially on his last contract, wanted more protection than a one-year deal.

For several years now, the Bengals have been reluctant to give him long-term security based on his age. The Bengals didn't want to mortgage their future salary cap by giving a huge deal to a player who is the oldest at his position in the NFL.

The Bengals tried to plan for this day, looking to the future by drafting tackles Cedric Ogbuehi and Jake Fisher in the first and second rounds of the 2015 draft. But Whitworth was just too good to lose his spot, and Ogbuehi and Fisher weren't good enough to even challenge him for it.

To understand what happened, it would be necessary to go back to 2015, when Whitworth and the Bengals were trying to negotiate a contract extension. The talks dragged on through September of that year before the Bengals gave in and gave Whitworth a one-year, $9 million extension.

The Bengals' reluctance to move forward with the negotiations did not sit well with Whitworth's camp. It was a bitter taste that lingered.

It appeared that both sides were moving forward when the Bengals made offers to Whitworth's representatives in the weeks leading up to free agency, but they did not take the necessary steps to ensure he would not leave for another team.

A source close to Whitworth wondered why the team did not place the franchise tag ($14.8 million for one year), or transition tag ($12.6 million) on him. The transition tag would have allowed them to assess Whitworth's value while having the opportunity to match, while the franchise tag, though expensive if Whitworth actually played on it, could have protected their investment while they continued to negotiate.

The Bengals did neither.

Now the team is essentially left scrambling. They continue to express optimism in Ogbuehi and Fisher, who were drafted with the idea that they would be the tackles of the future. Neither has come close to looking like a full-time starter.

Ogbuehi struggled so much at right tackle that the team resorted to rotating him with veteran Eric Winston before finally benching him. They moved Whitworth to guard for one game so they could see if Ogbuehi could play left tackle, which he said was his natural position.

It didn't go much better on that side.

With Whitworth gone, the Bengals have lost the longest-tenured player in their locker room, a valuable leader and the best player on their offensive line.

The team might have balked at paying one of their oldest players so much money, but last year proved Whitworth, who made the Pro Bowl as an alternate, is still as good as he ever was. They should have gritted their teeth and made every effort to match.

Now they're left watching as one of their best players suits up elsewhere.