Mitch Marner was traded to the Vegas Golden Knights — with an eight-year extension in place, sources told ESPN on Monday. Forward Nicolas Roy will go to the Toronto Maple Leafs in return.

Marner’s new deal has a $12 million average annual value, according to sources. Marner, 28, was the biggest name entering Tuesday’s NHL free agency, and multiple teams were hoping to make pitches. Marner was the NHL’s fifth-leading scorer last season with 102 points — 36 more than the next-closest free agent. The winger was drafted by his hometown Maple Leafs with the No. 4 pick in 2015.

The Maple Leafs knew that Marner was looking to test free agency at the end of the season. Over the past few days, Toronto worked with Vegas, which was Marner’s preferred destination, on a trade. The Maple Leafs held Marner’s rights until just before midnight Tuesday.

Had Marner become an unrestricted free agent, he couldn’t have signed a deal for more than seven years.

Marner finished a six-year deal that paid him $10.9 million annually. Marner, who played for Team Canada at Four Nations and likely will make their Olympic team, has 221 goals and 741 points in nine NHL seasons.

Toronto general manager Brad Treliving has stayed busy this week, re-signing John Tavares and Matthew Knies while trading for Utah forward Matias Maccelli earlier Monday.

Roy, 28, is a center who is entering Year 4 of a five-year deal that pays him $3 million annually.

Ahead of the Marner trade, the Golden Knights created cap space by sending defenseman Nicolas Hague to the Nashville Predators on Monday.

The deal makes Marner the highest-paid player on Vegas, however, center Jack Eichel ($10 million AAV) is entering the final year of his contract and is eligible to sign an extension this summer. The Golden Knights might not be done this offseason. According to sources, defenseman Alex Pietrangelo is expected to go on long-term injured reserve, which could create more flexibility.

Sign-and-trades ahead of free agency are becoming a trend for NHL teams that know they will not sign their coveted player; last season, the Carolina Hurricanes dealt Jake Guentzel’s rights to the Tampa Bay Lightning before he signed a seven-year deal.