BOSTON (CBS) — Celtics fans knew that Al Horford was most likely leaving in free agency this summer. That didn’t make Sunday evening any less excruciating.

After hearing various reports and rumors throughout the day that the Celtics might have been working toward re-signing the veteran big man, Celtics fans had to deal with the shock of seeing Horford sign with a divisional rival in Philadelphia.

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According to Adrian Wojnarowski, Horford agreed to sign a four-year, $109 million contract with the 76ers.

For the Celtics organization and their fans, that one’s going to hurt.

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The 33-year-old Horford spent the last three seasons in Boston, where he averaged 13.5 points, 7.0 rebounds, 4.6 assists, and 1.2 blocks per game. He earned a spot on the All-Star team in 2018, his fifth career appearance, and also was named to the Second Team All-Defensive Team that same year.

Part of Horford’s time in Boston was spent helping the Celtics get the better of the 76ers for three years. Now, he’ll be switching sides.

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Wojnarowski reported that the Celtics did offer a four-year deal to Horford, but with less guaranteed money.