(Alex Brandon/AP)

Major League Baseball Commissioner Rob Manfred will throw out the ceremonial first pitch at Nationals Park this afternoon. He is also expected to make official baseball’s worst kept secret — Nationals Park will host the 2018 All-Star Game.

Fans at Saturday’s exhibition game against the Yankees may have noticed a red banner beneath the Red Loft. Several fans indicated that the words behind the banner read “Home of the 2018 All-Star Game.”

D.C. has hosted the all-star game four times previously, the last time in 1969. Here’s how The Post reported on the announcement — which sometimes came as a genuine surprise — that D.C. was awarded each game.

1937 All-Star Game – Griffith Stadium (Announced July 6, 1936)

Shirley Povich had the news:

Griffith Stadium in Washington was unexpectedly designated tonight as the scene of the 1937 All-Star big league baseball game by the advisory committee of the two major-leagues.

Departing from the four-year custom of alternating the East and West as the sites of the major leagues’ All-Star spectacle, the committee accepted the invitation of Clark Griffith, owner of the Nats, to stage the game in Washington.

Detroit was known to be bidding for the 1937 game and was believed assured of it inasmuch as the contest this year was staged in the East, but Griffith pointed out the fitness of holding the contest in the Nation’s Capital.

The game, which in its four years’ history has come to be regarded as the greatest feature of each season, doubtless will be played in early July next year, as has been customary.

1956 All-Star Game – Griffith Stadium (Announced in 1955)

Two months after Senators owner Clark Griffith’s death in October 1955, it was announced that the 1956 All-Star game would be dedicated to him.

For the first time in its 34-year history, the major leagues’ All-Star game next summer will be dedicated to the memory of one of the great figures of baseball. The two major leagues today voted unanimously to designate the 1956 contest as the Clark Griffith Memorial game. It will be played in Washington on July 10, in Griffith Stadium, which bears the name of the late owner of the Washington club, who in 1901 was a cofounder of the American League.

1962 All-Star Game – D.C. Stadium (Announced June 27, 1961)

The major leagues today awarded the 1962 all-star game to the Washington Senators.

The action was taken at the request of Pete Quesada, president of the new American League team. Quesada personally presented the request at the joint meting of the National and American leagues.

The award of the 1962 game to Washington will enable the New Nats to present one of baseball’s top attractions in the $22 million stadium now being completed.

1969 All-Star Game – RFK Stadium (Announced March 20, 1968)

The 1969 All-Star baseball game was awarded to Washington, in a surprise announcement by Commissioner William D. (Spike) Eckert today.

Eckert noted that major league baseball will be observing its centennial next year and said, “Playing the game in the Nation’s Capital will be wonderful for baseball.”

The Cincinnati Reds of 1869 were the first team formed in the sport. Three previous All-Star games were played in Washington in 1937 and 1956 at Griffith Stadium and in 1962 at D.C. Stadium.

The announcement came as a complete surprise. There had been no hint that Washington would be the site in the near future. In the rotating system used for selecting cities for the All-Star game, Washington appeared at least a dozen years away from hosting another game.

Exceptions have been made to play the game in new stadiums. That is why Washington got the 1962 game, just six years after the 1956 All-Star game in Griffith Stadium.

With many new stadiums being built and new franchises being awarded, many expected Washington to have to wait as long as 18 years for another midseason classic.