On November 3, 2008, Billups was traded to the Denver Nuggets, along with Antonio McDyess and Cheikh Samb, for Allen Iverson. Pistons GM Joe Dumars said that it was "the hardest and toughest" move he had made as a general manager, describing Billups as "... a guy that I have looked at as a little brother."  Billups chose the #7 jersey to honor Denver Broncos quarterback John Elway, since two of his other favorite numbers, 1 and 4, were already worn by J. R. Smith and Kenyon Martin, respectively. He played his first game of the Nuggets' 2008-09 season on November 7, 2008. He recorded 15 points, four rebounds and three assists in 30 minutes of play in a 108-105 Nuggets' home win. He finished the season averaging 17.7 points, and 6.4 assists per game.  With Billups and Carmelo Anthony, the Nuggets accomplished a number of franchise milestones. Their 54-28 record matched a franchise record, and their 27-14 start was also a franchise record for wins in the first half of a season. This also marked the first time in the franchise's history the team had gotten 50 wins in back-to-back seasons. They led the Northwest division for much of the season, eventually winning the division and gaining the number two seed in the Western Conference, matching the highest the team had ever been seeded for the playoffs. In the first round, they defeated the New Orleans Hornets in 5 games, which included a record-equaling 58-point margin-of-victory. Billups also set a Nuggets franchise record with the most 3 pointers in a playoff game with 8, and his 19 3-pointers in total is also a Nuggets record for threes made in a playoff series. In his first year with the Nuggets, Billups led them back to the NBA Conference Finals for the first time since 1985. They would play the Lakers for the second straight year (the Lakers had swept them in the first round the year before). The Nuggets would ultimately lose the series 4-2. This was Billups' 7th straight conference finals. He joined Magic Johnson, Michael Cooper, Kareem Abdul-Jabbar, and Kurt Rambis as the only players to accomplish this feat since the Boston Celtics of the 1950s and 1960s led by Bill Russell. Billups finished the season sixth in voting for the 2009 NBA Most Valuable Player Award. He was also selected to his second All-NBA Third Team.  For the 2009-10 season, Billups reverted to wearing #1, the same number he wore with the Pistons. Teammate J. R. Smith, who had previously worn #1 since being acquired by the Nuggets in 2006, changed to the #5 jersey. On November 27, 2009, in the Nuggets' 128-125 win over the New York Knicks, Billups scored 32 points while teammate Carmelo Anthony scored 50. This made them only the third duo in NBA history to score at least 30 and 50 points respectively. On February 5, 2010, Billups set a career high in points with a 39-point performance in a road win over the Los Angeles Lakers with 27 of them coming from 9 three-pointers. During the 2010-11 season, he averaged 16.5 points per game, 5.3 assists per game, and 2.5 rebounds per game in 32.3 minutes per game. His .441 three point field goal percentage was a career high.

Answer this question "Why did Billups return to the Denver Nuggets?" by extracting the answer from the text above.
Billups was traded to the Denver Nuggets, along with Antonio McDyess and Cheikh Samb, for Allen Iverson.