Welch's daughter Kelly turned to social media to express her feelings about her father during this very difficult time:
Welch, 57, went 211-146 with a 3.47 ERA over a 17-year playing career that saw him appear in two All-Star Games a decade apart (1980 and 1990).
A two-time World Series champion as a player, first with the Los Angeles Dodgers in 1981 and then with the Oakland A's in 1989, Welch picked up a third ring as the pitching coach for the Arizona Diamondbacks in 2001.
His passing comes as a surprise, especially for those who saw him recently, as John Shea of the San Francisco Chronicle had:
MLB.com's Jane Lee had Oakland general manager Billy Beane's reaction to the news:
Her colleague, Jesse Sanchez, conveyed Arizona president Derrick Hall's thoughts:
Welch is perhaps best remembered for his Cy Young Award-winning season in 1990, when he went 27-6 with a 2.95 ERA for the A's, the last pitcher in baseball to win at least 25 games. For many of us who were growing up with the game in that era, Welch winning 27 games in one season was just about the coolest thing we'd ever seen a pitcher do.
Hall of Fame closer Dennis Eckersley, who played with Welch in Oakland from 1988-1994, was stunned:
It wasn't only Welch's former teammates who took to Twitter to express their condolences. Jeremy Barfield, a pitcher with Oakland's High-A affiliate in Stockton, paid respect to a man he got to know in spring training:
Welch is survived by his 18-year-old daughter, Kelly, two sons, Dylan (25) and Riley (23), and Mary Ellen, his former wife.