MIAMI – Ray Allen has played in Boston as an opponent 15 times. He knows what it’s like to play under the fabled Celtics banners, knows exactly how the crowd treats visiting players.

His 16th appearance as a visitor will be much different.

Not only will his trip there Sunday be his first as a former Celtic, but it will come with him donning the colors of perhaps the team’s biggest rival these days, the Miami Heat, who ousted Boston from the playoffs each of the last two seasons.

And make no mistake, Allen has been getting ready for everything that will accompany this trip for quite a while.

“I’ve thought about it,” Allen said. “I think more about who, family-wise, is going, who can go and sorting the whole protocol. I don’t know what to expect from their side. But it’s an interesting concept because I’ve always gotten a warm welcome, even before I started playing there. I just want to win. Everything else will take care of itself.”

When he played there as an opponent in the past, Allen typically got warm receptions. He starred at Connecticut and has deep roots in New England, and those two things go a long way in generating respect from the Boston fan base.

Then he joined the Celtics in the summer of 2007. A year later he helped them win a championship. He bled green.

Now, not so much.

So on a Sunday afternoon before a national television audience, the big story won’t be the return of the Heat to the site of their season-saving Game 6 win in the Eastern Conference finals last year, or the first trip back to Boston for LeBron James since his epic 45-point performance in that game, or even the memory of how Celtics fans cheered wildly for the last few minutes of that blowout loss as a “thank you” to their team.

“It’s going to be all about Ray,” Heat forward Chris Bosh said. “Celtic fans, they’re fixated on the rivalry and ‘How could you do that?’ They’re passionate.”

Allen’s relationship with the Celtics broke down in some respects last season, and when the Heat made him an offer last summer, he eventually accepted, knowing it would raise the ire of those back in Boston.

When the Celtics visited the Heat on opening night this season, the proof of the frosty relationships was there. Former teammates, Kevin Garnett and Paul Pierce especially, seemed to want nothing to do with Allen. As Allen checked into the game, his first official appearance as a Miami player, he approached Celtics Coach Doc Rivers and got a warm embrace.

It’s anyone’s guess what the scene will be Sunday.

“I’ll savor it, going back and seeing the people you spent so much time with,” Allen said. “But if you’re going into a situation thinking about negative perceptions or behavior that’s unbecoming of good sportsmanship, then you just want to get it over with, win the game and get out of there. I don’t want it to distract these guys from everybody doing their job and being ready to play.”