Diego Rodriguez Velazquez's portrait of King Philip IV. Research has revealed that this portrait is likely the first one Velazquez painted of King Philip IV. AP Photo/Meadows Museum

DALLAS (AP).- In preparing an exhibit on 17th century artist Diego Velazquez's early work for Spain's King Philip IV, art historians believe they discovered that a portrait by the Spanish master at Dallas' Meadows Museum is likely his first of his lifelong patron.

"Diego Velazquez: The Early Court Portraits" opens Sunday at the museum on the campus of Southern Methodist University, the result of a partnership between the Meadows and Madrid's famed Museo del Prado, Spain's national art museum. The exhibit, which the Meadows calls the most important devoted to Velazquez in the U.S. in more than two decades, will run through Jan. 13.

"What you'll see in this exhibition is the beginning of one of the most extraordinary relationships in the history of art — that's the relationship between young Velazquez and Philip IV," said Gabriele Finaldi, the Prado's deputy director for collections.

"What you need there is an extraordinarily talented artist, which you have in Velazquez. But you also need a very far-seeing patron, and that's Philip IV, who had real personal passion for painting," Finaldi added.

Velazquez became the king's court painter in 1623, when he was only 24. It was a job he would hold until his death in 1660 at the age of 61. The exhibit focuses on his first decade working for the king.

For the first time in four centuries, the Dallas exhibit brings together two of Velazquez's early portraits of the king: the Prado's full-length portrait of him dressed all in black that was painted in the 1620s and the Meadow's bust-length portrait.

In anticipation of the show, both portraits underwent analysis at the Prado. X-rays of the Meadows portrait showed brush strokes indicating Velazquez was working out how to paint the king, helping back up the belief that it could have been his initial attempt.

"Now we think more than ever that it was the first portrait," said Mark Roglan, director of the Meadows.

The exhibit features five paintings by Velazquez, including his portrait of the poet Luis de Gongora y Argote from the Museum of Fine Arts, Boston, which was done a year before Velazquez became Philip IV's court painter. A Velazquez portrait of a court jester painted in the early 1630s comes from the Cleveland Museum of Art.

A portrait of Philip IV from Velazquez's workshop that has never before been seen in public comes from a private Spanish collection. The exhibition also features 16 prints, some with engraved portraits modeled after Velazquez's work.

The Prado and the Meadows began a three-year partnership in 2009 that has included an exchange of scholars, research, works of art and exhibitions. This summer the two institutions announced they will extend the collaboration for another two years.

The Meadows Museum, which opened in 1965, is the vision of a Texan who started collecting Spanish art after being inspired by visits to the Prado. Hoping to create a "Prado on the Prairie," oil financier Algur H. Meadows donated his private Spanish art collection and funds to start the museum to SMU. The Meadows' portrait of Philip IV was one of his acquisitions.

"It was a very easy and natural fit that the Prado should work closely with the Meadows," Finaldi said.

By: Jamie Stengle, Associated Press. Copyright 2012 The Associated Press.