CHICAGO — The Chicago Cubs already boasted one of the best young cores in baseball – and that was before they added one of the top outfielders.

Free agent Jason Heyward agreed to a $184 million, eight-year contract with the Cubs, according to a person familiar with the negotiations.

The person spoke Friday on the condition of anonymity because the deal has not been announced.

The agreement with the three-time Gold Glove winner is the latest in a series of big moves by the Cubs as they try to build on a breakthrough season and bring home their first World Series title since 1908. The Cubs won 97 games and reached the NL Championship Series before getting swept by the New York Mets.

Chicago also has added pitchers John Lackey and Adam Warren along with infielder Ben Zobrist. Lackey, like Heyward, left the rival Cardinals for the Cubs and figures to be Chicago’s No. 3 starter behind NL Cy Young Award winner Jake Arrieta and Jon Lester.

An All-Star in 2010, the 26-year-old Heyward hit .293 with 13 homers and 60 RBI this year, helping St. Louis win the NL Central. He spent his first five big league seasons with Atlanta.

Chicago also signed Zobrist to a $56 million, four-year contract and traded Starlin Castro to the New York Yankees for Warren.

Heyward has a .268 career batting average and has hit more than 18 home runs just once. But the Cubs are counting on him to help strengthen a batting order that includes young sluggers Anthony Rizzo, Kris Bryant and Kyle Schwarber along with Addison Russell. All are 26 or younger.

The Cubs also are counting on Heyward to help solidify their outfield, whether they keep him in right field or move him to center. If Heyward plays right, they could try to trade Jorge Soler for a pitcher or center fielder.

ASTROS: Tony Sipp agreed to an $18 million, three-year contract to remain with Houston. The 32-year-old left-hander had a career-best 1.99 ERA in 60 games last season. He was 3-4 with 62 strikeouts in 541/3 innings.

NATIONALS: Rebuilding its middle relief corps, Washington agreed with right-hander Shawn Kelley on a three-year contract and with left-hander Oliver Perez on a two-year deal.

Kelley, 31, was 2-2 with a 2.45 ERA in 53 appearances for the San Diego Padres last season.

Perez, 34, who previously was with the Nationals’ Double-A Harrisburg affiliate, was a combined 2-4 with a 4.17 ERA in 70 games with the Diamondbacks and Astros in 2015. His deal with Washington is worth $7 million.

BLUE JAYS: Infielder Darwin Barney agreed to a $1.05 million, one-year contract. The 30-year-old hit .304 with two homers in 15 games for Toronto after being acquired from the Dodgers on Sept. 13.